Step 1: Make the Pastry Cream Begin by heating 1 cup milk, 1 cup heavy cream, 1/3 cup granulated sugar, and 1/4 teaspoon salt in a saucepan until it simmers. In another bowl, whisk 5 large egg yolks with the remaining 3 tablespoons granulated sugar and 3 tablespoons cornstarch until smooth.

Step 2: Make the Pastry Cream Slowly add the hot milk mixture to the egg mix while stirring to avoid scrambling the eggs. Pour everything back into the saucepan and cook over medium heat until it thickens. Strain it, then mix in 1 teaspoon vanilla extract and 4 tablespoons unsalted butter until creamy.

Step 3: Make the Pastry Cream Cover the mixture with plastic wrap directly on the surface and let it cool before chilling for about 2 hours. This step ensures your boston cream cupcakes with custard filling have that authentic, smooth texture.

Step 4: Prepare the Cupcakes Preheat your oven to 350°F (175°C) and line your cupcake tins with liners. In a large bowl, beat 1/2 cup unsalted butter, 1/2 cup avocado oil, and 1 3/4 cups granulated sugar until fluffy. Add 4 large eggs one at a time, then stir in 2 teaspoons vanilla extract.

Step 5: Prepare the Cupcakes In a separate bowl, whisk together 3 cups all-purpose flour, 1 tablespoon baking powder, and 3/4 teaspoon salt. Alternate adding this dry mix and 1 1/4 cups buttermilk to the wet ingredients, starting and ending with the flour. Fill the liners about 3/4 full and bake for 17-19 minutes, or until a toothpick comes out clean.

Step 6: Prepare the Cupcakes Let the cupcakes cool completely on a wire rack. This part of making boston cream cupcakes sets the base for the delicious filling and glaze.

Step 7: Whip Up the Ganache Frosting In a microwave-safe bowl, combine 1 cup semisweet chocolate chips, 1/2 cup heavy cream, and 2 tablespoons light corn syrup if you want extra gloss. Heat in short intervals, stirring until smooth, then sift in 1/3 cup powdered sugar and let it cool until it’s thick but pourable.

Step 8: Assemble the Cupcakes Cut a cavity in each cooled cupcake, about 1 1/2 inches wide and 1 inch deep. Fill it with the chilled pastry cream using a piping bag, then top with the plug you cut out. Spoon the ganache over each one and let it set. For more on fillings, check out a detailed pastry cream guide.