Make the Pastry Cream (The Creamy Creation):

1. 1. Heat the Milk and Cream (The Milk Mixture Magic): In a medium saucepan, whisk together the whole milk, heavy cream, 1/4 cup of the granulated sugar, and the salt. Heat over medium heat, stirring frequently, until the mixture is steaming and the sugar is completely dissolved. Remove the saucepan from the heat and let the mixture cool for 10 minutes. This allows the flavors to meld and prevents the eggs from cooking too quickly when added.

1. 1. Prepare the Egg Yolks (The Yolk Yield): In a separate medium bowl, whisk together the egg yolks and the remaining 1/4 cup of granulated sugar until smooth and pale yellow. Whisk in the cornstarch until no lumps remain. This ensures a smooth and lump-free pastry cream.

1. 1. Temper the Egg Yolks (The Tempering Technique): Gradually whisk about 1/3 of the hot milk mixture into the egg yolk mixture, whisking constantly. This process, known as tempering, slowly raises the temperature of the egg yolks and prevents them from scrambling when added to the hot milk mixture.

1. 1. Combine and Cook (The Cooking Creation): Whisk the tempered egg yolk mixture back into the saucepan with the remaining hot milk mixture. Return the saucepan to medium heat and cook, whisking constantly, until the pastry cream thickens to a pudding-like consistency, about 2-3 minutes. Constant whisking is essential to prevent scorching and lumps.

1. 1. Strain and Finish (The Finishing Flourish): Strain the pastry cream through a fine-mesh sieve into a clean bowl. This removes any lumps and ensures a smooth and silky texture. Whisk in the vanilla extract and the softened unsalted butter until fully incorporated.

1. 1. Chill (The Chilling Charm): Press a piece of plastic wrap directly onto the surface of the pastry cream to prevent a skin from forming. Refrigerate the pastry cream until it is completely chilled, at least 2 hours, or preferably overnight.

Make the Cupcakes (The Cupcake Creation):

1. 1. Preheat and Prepare (The Preparation Phase): Preheat your oven to 350°F (175°C). Line two 12-count muffin pans with cupcake liners.

1. 1. Cream Butter and Sugar (The Creaming Commencement): In a large mixing bowl, using an electric mixer fitted with the paddle attachment, beat the softened unsalted butter, vegetable oil, and granulated sugar together until light and fluffy, about 2 minutes. This process incorporates air into the batter, making the cupcakes light and tender.

1. 1. Add Eggs and Vanilla (The Egg Emulsion): Beat in the eggs one at a time, allowing each egg to fully incorporate into the batter before adding the next. Then, beat in the vanilla extract until fully incorporated. Room temperature eggs combine more easily with the batter and create a smooth emulsion.

1. 1. Combine Dry Ingredients (The Dry Ingredient Duet): In a separate medium bowl, whisk together the all-purpose flour, baking powder, and salt.

1. 1. Combine Wet and Dry (The Wet and Dry Waltz): Alternate adding the dry ingredients and the buttermilk to the butter mixture in three additions, beginning and ending with the dry ingredients. Mix each addition just until combined. Overmixing can lead to tough cupcakes.

1. 1. Bake (The Baking Brilliance): Divide the cupcake batter evenly between the prepared cupcake liners, filling them about 3/4 full. Bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean or with just a few moist crumbs.

1. 1. Cool (The Cooling Conclusion): Allow the cupcakes to cool in the muffin pans for 10 minutes before transferring them to a wire rack to cool completely.

Make the Ganache Topping (The Ganache Glory):

1. 1. Melt Chocolate (The Chocolate Melting Moment): Place the semisweet chocolate chips, heavy cream, and light corn syrup (if using) in a microwave-safe bowl. Microwave in 20-second intervals, stirring well between each interval, until the chocolate is melted and smooth.

1. 1. Add Confectioners’ Sugar (The Sweetening Step): Sift the confectioners’ sugar into the melted chocolate mixture and whisk until fully incorporated.

1. 1. Thicken (The Thickening Time): Let the ganache sit at room temperature for 10-15 minutes to thicken slightly before using.

Assemble the Cupcakes (The Assembly Art):

1. 1. Cut Cavities (The Cavity Creation): Once the cupcakes are completely cooled, use a paring knife or a small melon baller to cut a cone-shaped cavity out of the center of each cupcake, going about 3/4 of the way down but not cutting through the bottom. Remove the cone portion of the cupcake.

1. 1. Fill with Pastry Cream (The Filling Fiesta): Transfer the chilled pastry cream to a piping bag fitted with a round tip. Pipe the pastry cream into each cavity, filling it to the top.

1. 1. Replace Cone (The Cone Connection): Replace the cone portion of the cupcake back on top of the pastry cream filling.

1. 1. Top with Ganache (The Ganache Grandeur): Spoon or drizzle the slightly thickened ganache over the tops of the filled cupcakes.

1. 1. Chill (The Final Chill): Refrigerate the assembled cupcakes until ready to serve. Boston Cream Cupcakes are best consumed within 4-5 days.