Boston Cream Pie Sheet Cake Recipe

<ul class="ingredients-main-list"><li class="ingredients-single-item">For the Cake:</li><li class="ingredients-single-item">300g all-purpose flour</li><li class="ingredients-single-item">2 tsp baking powder</li><li class="ingredients-single-item">1/2 tsp salt</li><li class="ingredients-single-item">225g unsalted butter, softened</li><li class="ingredients-single-item">350g granulated sugar</li><li class="ingredients-single-item">4 large eggs, room temperature</li><li class="ingredients-single-item">2 tsp vanilla extract</li><li class="ingredients-single-item">240ml whole milk, room temperature</li><li class="ingredients-single-item">For the Custard Filling:</li><li class="ingredients-single-item">500ml whole milk</li><li class="ingredients-single-item">1 vanilla bean, split and scraped (or 2 tsp vanilla extract)</li><li class="ingredients-single-item">100g granulated sugar</li><li class="ingredients-single-item">35g cornstarch</li><li class="ingredients-single-item">Pinch of salt</li><li class="ingredients-single-item">5 large egg yolks</li><li class="ingredients-single-item">30g unsalted butter, cold and cubed</li><li class="ingredients-single-item">For the Chocolate Ganache:</li><li class="ingredients-single-item">170g dark chocolate (60-70% cocoa), finely chopped</li><li class="ingredients-single-item">180ml heavy cream</li><li class="ingredients-single-item">30g unsalted butter</li><li class="ingredients-single-item">1 tbsp corn syrup (optional, for shine)</li></ul>

<ul class="equipment-main-list"><li class="equipment-single-item">33x23cm (13x9-inch) baking pan</li><li class="equipment-single-item">Stand mixer or electric hand mixer</li><li class="equipment-single-item">Medium saucepan</li><li class="equipment-single-item">Fine-mesh sieve</li><li class="equipment-single-item">Digital kitchen thermometer</li><li class="equipment-single-item">Offset spatula</li></ul>

<ol class="no-list-style"><li class="MethodStepper"><h4 class="step-title">Step 1</h4>Preheat your oven to 175°C (350°F). Grease your 33x23cm baking pan and line with parchment paper, leaving an overhang on the sides to easily lift the cake out later.</li><li class="MethodStepper"><h4 class="step-title">Step 2</h4>Start with the vanilla custard as it needs time to chill. In a medium saucepan, heat the milk and vanilla bean (if using) until steaming but not boiling. Meanwhile, in a heat-proof bowl, whisk together the sugar, cornstarch, salt, and egg yolks until well combined and slightly pale.</li><li class="MethodStepper"><h4 class="step-title">Step 3</h4>Slowly pour about one-third of the hot milk into the egg mixture while whisking constantly (this tempers the eggs, preventing them from scrambling). Then pour this mixture back into the remaining hot milk in the saucepan, whisking continuously.</li><li class="MethodStepper"><h4 class="step-title">Step 4</h4>Cook the custard over medium heat, whisking constantly, until it thickens and begins to bubble, about 4-5 minutes. Once it starts to bubble, continue cooking for 1 more minute to ensure the cornstarch is fully activated. The consistency should coat the back of a spoon, and when you run your finger through it, the line should hold.</li><li class="MethodStepper"><h4 class="step-title">Step 5</h4>Remove from heat and strain through a fine-mesh sieve into a clean bowl to remove any lumps. If using vanilla extract instead of bean, stir it in now. Add the cold butter cubes and whisk until melted and incorporated. Press plastic wrap directly onto the surface of the custard (this prevents a skin from forming) and refrigerate until cold, at least 2 hours or overnight.</li><li class="MethodStepper"><h4 class="step-title">Step 6</h4>For the cake, whisk together the flour, baking powder, and salt in a medium bowl. In the bowl of your stand mixer fitted with the paddle attachment (or using a hand mixer), cream the butter and sugar on medium-high speed until light and fluffy, about 3-4 minutes. This extended creaming creates air pockets that help the cake rise and achieve a tender crumb.</li><li class="MethodStepper"><h4 class="step-title">Step 7</h4>Add the eggs one at a time, mixing well after each addition and scraping down the sides of the bowl as needed. Beat in the vanilla extract. With the mixer on low speed, add the flour mixture in three parts, alternating with the milk, beginning and ending with the flour. Mix until just combined; overmixing will develop gluten and make your cake tough.</li><li class="MethodStepper"><h4 class="step-title">Step 8</h4>Pour the batter into your prepared pan and smooth the top with an offset spatula. Gently tap the pan on the counter a few times to release any large air bubbles. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean and the cake springs back when lightly touched.</li><li class="MethodStepper"><h4 class="step-title">Step 9</h4>Allow the cake to cool in the pan for 15 minutes, then use the parchment overhang to carefully lift it out onto a wire rack to cool completely. The cake must be absolutely cool before adding the custard, or it will melt.</li><li class="MethodStepper"><h4 class="step-title">Step 10</h4>Once the cake is completely cool, carefully slice it horizontally into two even layers using a large serrated knife. Place the bottom layer on your serving platter or cake board. Remove the chilled custard from the refrigerator and whisk it briefly to loosen if it's very firm. Spread the custard evenly over the bottom cake layer, leaving about a 1cm border around the edges (as the weight of the top layer will push the custard outward).</li><li class="MethodStepper"><h4 class="step-title">Step 11</h4>Gently place the top cake layer over the custard, pressing down very lightly to secure. If any custard squeezes out, simply wipe it away with a spatula. Place the assembled cake in the refrigerator while you prepare the ganache.</li><li class="MethodStepper"><h4 class="step-title">Step 12</h4>For the chocolate ganache, place the finely chopped chocolate in a heat-proof bowl. In a small saucepan, heat the heavy cream just until it begins to simmer around the edges (do not boil). Pour the hot cream over the chocolate and let it sit for 1 minute to soften the chocolate. Gently stir until smooth and all chocolate is melted. Add the butter and corn syrup (if using) and stir until completely incorporated and glossy.</li><li class="MethodStepper"><h4 class="step-title">Step 13</h4>Allow the ganache to cool for about 5-10 minutes until it thickens slightly but is still pourable. The ideal temperature is around 32-35°C (90-95°F) – it should coat the back of a spoon but still flow easily. Pour the ganache over the center of the cake and use an offset spatula to gently spread it to the edges, allowing some to drip down the sides for a beautiful finish.</li><li class="MethodStepper"><h4 class="step-title">Step 14</h4>Return the cake to the refrigerator for at least 1 hour to set the ganache and firm up the custard. For the best texture and flavor, remove the cake from the refrigerator about 20-30 minutes before serving to take the chill off.</li><li class="MethodStepper"><h4 class="step-title">Step 15</h4>To serve, use a sharp knife dipped in hot water and wiped dry between cuts for clean slices. Store any leftovers covered in the refrigerator for up to 3 days, though the cake is best enjoyed within the first 2 days while the custard remains fresh and the cake remains moist.</li></ol>