Boston cream pie is not a pie at all; it’s a cake. In the mid-19th century, the layered sweet was traditionally baked in pie tins, hence the name. In this icy version, we’ve swapped out the vanilla pastry cream for custardy vanilla ice cream and added an extra layer of chocolate ganache for good measure.
Game plan: Make sure you have enough room in your freezer before you begin. You’ll need a flat area at least 10 by 10 by 5 inches to accommodate the cake comfortably, depending on the size of the flat dish or baking sheet holding it.
To slice the frozen cake, warm a sharp knife in hot water for about 30 seconds, then use a kitchen or paper towel to dry the knife. Slice the cake while the knife is still warm, pushing the knife down into the cake and slowly removing it. Clean the knife off and repeat warming, drying, slicing, and cleaning with each cut into the cake. If the cake is still too frozen to easily slice, let it sit for another 5 minutes.
This recipe was featured as part of our Make Your Own Ice Cream Treats project.
- 1Heat the oven to 350°F and arrange a rack in the middle. Coat an (8-inch) cake pan generously with butter, then flour, tapping out any excess flour; set aside.
- 2Whisk flour, baking powder, and salt in a medium bowl to combine; set aside.
- 3In the bowl of a stand mixer fitted with a whisk attachment, combine oil, water, vanilla, egg yolks, and 1/2 cup plus 2 tablespoons of the sugar. Whisk on medium speed until mixture is light in color and looks slightly thickened, about 5 minutes. Turn off the mixer and, using a rubber spatula, scrape down the sides of the bowl. Add reserved dry ingredients, turn the mixer to low, and whisk until smooth, about 1 minute. Transfer batter to a large bowl.
- 4Wash and dry the mixer bowl and whisk attachment. Place egg whites in the bowl and whisk on high speed until soft peaks form (they should droop over like soft-serve ice cream), about 30 seconds. Gradually add the remaining 2 tablespoons sugar and continue whisking until stiff peaks form (they should stand straight up), about 1 minute more. Using a rubber spatula, fold a quarter of the egg whites into the batter until evenly incorporated; gently fold in the remaining egg whites until just combined and no large white streaks remain.
- 5Pour the batter into the prepared pan. Bake until the surface of the cake is golden brown and springs back when pressed and a toothpick or cake tester inserted into the center comes out clean, about 25 to 30 minutes. Place on a wire rack to cool slightly, about 15 minutes. Carefully run a knife around the perimeter and turn the cake onto the rack to cool completely.
For the ganache:
- 1Place chocolate in a medium heatproof bowl; set aside.
- 2Place cream in a small saucepan over medium heat and bring to a simmer. Pour over chocolate and let stand until chocolate has softened, about 5 minutes.
- 3Add butter and stir until smooth. Let cool slightly before using.
- 1Place ice cream in the refrigerator until slightly softened, about 30 minutes. Place the cooled cake in the refrigerator to chill, about 30 minutes. (Chilling the cake ahead of time will prevent the ganache from streaking.)
- 2Meanwhile, cut a 30-inch-long piece of parchment or waxed paper and fold it lengthwise until it is 4 inches wide. Place a small saucepan of water over low heat and bring to a simmer.
- 3Once the cake is chilled, slice it horizontally into 2 equal disks. Place the top half of the cake cut side up on a large, flat dish or baking sheet. Return the second half to the refrigerator. Tightly wrap the parchment strip around the perimeter of the cake so that it is flush with the dish or baking sheet, to make a collar. Tape to secure. (The collar will keep the ganache and ice cream from running over the side of the cake.)
- 4Measure 1 1/4 cups of the warm ganache and pour it over the parchment-wrapped cake, tilting the dish or baking sheet until the ganache reaches the parchment collar and evenly coats the top. Place the cake on a flat, even surface of the freezer until the ganache has set, about 15 minutes. Place the bowl of remaining ganache over the saucepan of simmering water; remove the saucepan from heat.
- 5Remove the softened ice cream from its container and transfer to a large bowl. Stir with a rubber spatula or wooden spoon until it is spreadable but not liquidy. Working quickly, spread the softened ice cream over the ganache (leaving any melted ice cream in the bowl), smoothing it into an even layer until it reaches the parchment collar.
- 6Remove the bottom cake half from the refrigerator and fit it cut side down inside the parchment collar and on top of the ice cream, then press lightly. Remove the bowl of ganache from the saucepan, dry any condensation that has formed on the bottom of the bowl, and stir until smooth. Pour the remaining ganache over the top of the cake and tilt the dish or baking sheet to evenly coat. Immediately place the cake in the freezer until the ice cream is firm, at least 3 hours.
- 7When ready to serve, remove the cake from the freezer, remove the parchment collar, and let the cake sit for 15 to 20 minutes before slicing. If not serving immediately, remove it from the freezer once completely frozen, remove the parchment collar, wrap the cake entirely in plastic wrap, and store in the freezer for up to 1 week.