1 1/3 cups heavy cream
3 large egg yolks
1/3 cup sugar
1 tablespoon plus 1 teaspoon cornstarch
2 tablespoons cold unsalted butter, cut into 2 pieces
1 1/2 teaspoons vanilla
1 3/4 cups all purpose flour
1 1/2 teaspoon baking powder
3/4 teaspoon salt
1 cup sugar
12 tablespoons unsalted butter, softened but still cool, cut into 12 pieces
3 large eggs
3/4 cup milk
1 1/2 teaspoons vanilla extract
3/4 cup heavy cream
1/4 cup light corn syrup
8 ounces bittersweet chocolate, chopped
1/2 teaspoon vanilla
Heat cream in a medium saucepan over medium heat until simmering, stirring occasionally. Meanwhile, whisk egg yolks, sugar and salt together in medium bowl. Add cornstarch and whisk mixture until mixture is pale yellow and thick, about 15 seconds. When cream reaches full simmer, slowly whisk into yolk mixture. Return mixture to saucepan and cook over medium heat, whisking constantly until thick and glossy, about 1 1/2 minutes. Off heat, whisk in butter and vanilla. Transfer pastry cream to small bowl, press plastic wrap directly on surface, and refrigerate until cold and set at least 2 hours or up to 2 days.
Adjust oven rack to middle position and heat oven to 350º. Spray muffin tin with cooking spray, flour generously, and tap pan to remove excess flour.
With electric mixer on low speed, combine flour, baking powder, salt and sugar in large bowl. Add butter, one piece at a time and combine until mixture resembles course sand. Add eggs one at time, and mix until combined. Add milk and vanilla, increase speed to medium and mix well until light and fluffy and no lumps remain, about 3 minutes. Fill muffin cups three-quarters full. Bake until toothpick inserted in center of cupcake comes out clean, 18 to 20 minutes. Cool cupcakes in pan 5 minutes then transfer them to rack to cool completely.
Cook cream, corn syrup, chocolate and vanilla in a small saucepan over medium heat, stirring constantly, until smooth. Cool and thicken for 30 minutes.
PUTTING CUPCAKES TOGETHER
Insert the tip of a small knife at 45 degree angle and about 1/8 inch from the edge of the cup cake and cut all the way around, removing a cone-shaped section of cake. Cut away all but the top 1/4 inch of the cone, leaving only a small disk of cake. Fill the cupcake with 2 tablespoons pastry cream and top with the disk of cake. Set the filled cupcakes on a wire rack set over parchment paper. Spoon 2 tablespoons of glaze over each cupcake, allowing it to drip down the sides. Can be refrigerated for up to 2 days; bring to room temperature before serving.