Cocoa-Coffee Boston Cream Pie

This week’s spin on a classic American dessert: Boston Cream Pie! Not a pie at all, Boston Cream Pie typically consists of two layers of yellow sponge cake filled with pastry cream and topped with a chocolate glaze. My version is amped up by the bitterness of chocolate and coffee, which are featured in both the cake and the topping. I leave the filling vanilla, but convert the pastry cream into a french-style crème diplomat by folding in some whipped cream, giving it a lightness not found in standard pastry cream. I also replace the more typical sponge cake with a butter cake that utilizes Rose Levy Beranbaum's reverse-creaming method, resulting in a rich, tender, moist cake. The light, creamy custard contrasts beautifully with the deeply chocolatey, coffee infused cake for a stellar, balanced dessert. This recipe features several components, but all can be made in advance to lighten the workload. In fact, I would recommend making the cake layers and the pastry cream the day before you plan to serve this. That way, you can assemble the cake that morning and refrigerate it until it’s serving time.

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History

Boston cream pie is commonly attributed to Boston’s famed Parker House Hotel, but as with the histories of many foods, the typically cited origin story is rather dubious. According to Stella Parks’ excellent 2017 book Bravetart, the association between the Parker House and this dessert had not been established until 1946, well after the popularization of the cake we now call Boston Cream Pie. The erroneous naming of this “pie” was not uncommon during the era of its inception: there were numerous similar 19th century desserts, all filled and unfrosted, referred to by names like “Washington Pie.” The name is thought to derive from the pan the cake was baked in: a shallow metal pie tin. Cakes filled with custard were fairly common during this time period, and were typically referred to as “cream pies.” The distinguishing feature of the Boston Cream Pie was the chocolate glaze, thought to be a ritzy and expensive adornment (suitable for impressing the guests of the Parker House) on what is really a fairly simple, homey dessert.

A 1959 advertisement for Betty Crocker Boston Cream Pie mix.

Whether this claim is accurate is debatable; this topping could just as easily have derived from a newspaper or an advertisement as having been developed by the Parker House. Regardless of its origins, the combination results in a charmingly rustic yet undeniably decadent dessert.

The Recipe: Cocoa-Coffee Boston Cream Pie

Ingredients:

For the cake:

Dutch-processed cocoa powder, 63g (¾ cup)

Freshly brewed coffee, 236g (1 cup)

3 eggs

Pure vanilla extract, 1 teaspoon

Instant espresso powder, 1 teaspoon

All-Purpose flour, 200g (1 ⅔ cups)

Cornstarch, 47g (scant ½ cup)

Granulated sugar, 300g (1 ½ cups)

Baking powder, 1 tablespoon

Kosher Salt, ¾ teaspoon Morton or 1 ½ teaspoons Diamond Crystal

Unsalted butter, room temperature, 2 sticks (226g)

For the pastry cream filling:

Whole milk, 456g (2 cups)

Granulated sugar, 100g (½ cup)

Kosher salt, ¼ teaspoon Morton or ½ teaspoon Diamond Crystal

Cornstarch, 30g (¼ cup)

5 egg yolks, (~80g)

Unsalted butter, 6 tablespoons (85g)

Pure vanilla extract, 2 teaspoons

For the cake soak:

Granulated sugar, 67g (⅓ cup)

Water, 75g (⅓ cup)

Instant espresso powder, 1 teaspoon

For the ganache:

Bittersweet chocolate, ~60% cocoa solids, 113g (4oz), finely chopped

Heavy cream, 113g, (½ cup)

To assemble:

Heavy Cream, 113g (½ cup)

To make the cake:

Grease two 9-inch cake pans with butter, baker’s spray, or neutral oil and line with parchment paper. Set aside.

In a medium bowl, combine the cocoa powder and coffee and set aside until it cools to room temperature or is just slightly warm. Combining the cocoa with hot liquid blooms it and brings out the flavor.

In another bowl, whisk together the eggs and vanilla. While whisking constantly, slowly stream in about ¼ of the cocoa mixture. Set aside.

In a large bowl with a hand mixer or the bowl of a stand mixer fitted with the paddle attachment, mix the flour, cornstarch, sugar, baking powder, and salt until combined. Add the butter and the reserved 3⁄4 of the cocoa mixture and mix on low speed until you no longer see any bits of dry flour. Gradually increase the speed to medium-high and beat for 90 seconds to begin to develop the gluten in the flour. Cutting this time short could lead to the cake collapsing when baked. Scrape down the sides of the bowl and beat in the egg mixture in three additions, mixing for 20 seconds after each addition. Scrape the batter into the prepared pans.

Bake for 25 to 35 minutes or until the cake springs back when lightly poked and a skewer inserted into the center comes out with just a few moist crumbs. Allow to cool completely before filling and stacking the layers. The cakes can be made and stored wrapped in plastic for up to 2 days before assembly.

To make the filling:

In a medium saucepan set over medium heat, bring the milk to a gentle simmer, stirring occasionally and scraping the bottom to prevent the milk from scalding. The milk is ready when it’s steaming and just starting to form small bubbles on the surface. Remove from heat and set aside while you beat the eggs.

In a large bowl, combine the egg yolks, salt, sugar, and cornstarch and whisk vigorously until the mixture pales in color and thickens in texture. When the mixture drips off of the whisk back into the bowl, it should briefly settle on the surface of the liquid before disappearing (see photo above).

While whisking constantly, slowly stream in the hot milk into the egg mixture. Once about three quarters of the milk has been added, pour the mixture into the saucepan and whisk to combine.

Have a clean, empty bowl handy by the stove. Set the pot back on medium heat and cook, whisking constantly, until the mixture thickens. It should easily hold the marks of the whisk and when you stop whisking you should see large, slowly popping bubbles beneath the surface of the custard. Depending on the peculiarities of your stove and the pot you’re using, this should take somewhere between 3 and 6 minutes. Once the mixture has noticeably thickened and you see bubbling, remove from heat and immediately scrape into the reserved medium bowl. Don’t scrape the bottom of the pot when transferring the custard to the bowl, as that is where curdling is most likely to happen. You don't want scrambled eggs in your filling!

While the custard is still hot, add the butter one tablespoon at a time and whisk until fully incorporated and smooth. If the butter has been incorporated but you can still see some lumps in the custard, strain through a fine mesh sieve. Whisk in the vanilla.

Press a sheet of plastic wrap directly against the surface of the custard and refrigerate until cold, at least 3 hours. The custard can be refrigerated for up to 3 days before use.

The texture of finished pastry cream.

To make the soak:

In a small saucepan set over medium-high heat, combine the water and sugar and bring to a simmer. Add the instant espresso powder and stir to dissolve. Set aside to cool completely. The soak can be refrigerated for up to 5 days.

To make the ganache:

In a small saucepan set over medium heat, bring the cream to a simmer. Place the chocolate in a heatproof bowl and pour the hot cream over it. Allow to stand for 5 minutes to allow the chocolate to melt. After 5 minutes, stir to combine until smooth and glossy. Refrigerate the mixture until cool, about 30 minutes. With a hand or stand mixer, whip on medium-high until the mixture has a spreadable frosting-like texture. Use immediately.

To assemble:

At this point, all of the components should be made. The cake should be cooled, the custard for the filling should be cold, the soak should have cooled, and the ganache should be whipped and spreadable.

Finish the filling by stirring the cooled custard to smooth it out and ensure that it’s easily spreadable. Place the cream in a medium bowl or the bowl of a stand mixer fitted with the whisk attachment and whip until it holds stiff peaks. You can do this with a stand mixer, a hand mixer, or by hand with a whisk. Be careful not to overwhip, stopping just when the cream holds a firm peak when the whisk or beater is pulled straight up from the bowl. Gently fold the whipped cream into the custard with a flexible spatula.

If the cake domed significantly in the oven, level it. To do this, use a serrated knife to carefully score a circle around the perimeter of the cake where the straight edge meets the domed top. Then, using long, smooth sawing motions, follow the guide to cut all the way through the cake, removing the top. If your cake has a reasonably flat top (a small dome is fine), feel free to skip this.

Place one of the cake layers right-side-up on a serving plate. Using a pastry brush or a spoon, apply half of the soak to the surface of the cake. Don’t be shy, the cake can take it! Now, spread the filling mixture onto the center of the cake, spreading it into an even layer that nearly reaches the edge. Leave a ¾ inch uncovered border around the edge of the cake, as the filling will squish outward when you apply the top layer. Apply the top layer upside down so that the flat bottom of the cake faces up. Gently press down to make sure that the cake adheres to the filling underneath. Apply the remaining half of the soak to the surface of the second layer. Finally, spread the whipped ganache onto the top of the cake and swoosh decoratively with the back of a spoon if desired. Place the cake in the refrigerator for at least two hours for everything to adhere and set before slicing and serving. This cake is best cut with a knife run under hot water and dried before slicing. The heat will minimize resistance and prevent the filling from squishing out. The finished cake will keep, covered airtight in the refrigerator, for up to 3 days.

Resources

Beranbaum, Rose Levy. The Cake Bible. New York, NY: Houghton Mifflin Harcourt, 1988.

Finn, Carina. “Bake a Forgotten 19th-Century Presidential 'Pie'.” Atlas Obscura. Atlas Obscura, May 18, 2021. https://www.atlasobscura.com/articles/what-is-washington-pie.

Parks, Stella. Bravetart: Iconic American Desserts. W.W. Norton & Company, 2017.

Saffitz, Claire. Dessert Person: Recipes and Guidance for Baking with Confidence. New York: Clarkson Potter/Publishers, 2020.