2tablespoonsunsalted butterchilled and cut into 2 pieces
For the Cupcakes:
12tablespoonsunsalted buttersoftened but still cool, cut into 12 pieces
The Pastry Cream:
Heat the heavy cream in a medium saucepan over medium heat until simmering, stirring occasionally.
Meanwhile, whisk the egg yolks, sugar and salt together in a medium bowl.
Add the cornstarch and whisk until the mixture is pale yellow and thick, about 15 seconds.
When the cream reaches a full simmer, slowly whisk it into the yolk mixture.
Return the mixture to the saucepan and cook over medium heat, whisking constantly, until it's a thick pudding consistency, 1 to 2 minutes.
Remove the pan from the heat and whisk in the butter and vanilla extract until the butter is completely melted.
Transfer the pastry cream to a small bowl and press plastic wrap directly on the surface. Refrigerate until set, at least 2 hours or up to 2 days.
Preheat oven to 350 degrees F.
Line a standard 12-cup muffin pan with paper liners and set aside.
In the bowl of a stand mixer fitted with paddle attachment, combine the flour, sugar, baking powder and salt on medium-low speed.
Add the butter and mix until the mixture resembles coarse sand.
Add the eggs, gently mixing until incorporated.
Add the milk and vanilla extract; to avoid splatter, blend on low and then increase to medium, mixing until light and fluffy and no lumps remain, about 3 minutes, stopping to scrape the sides and bottom of the bowl halfway through.
Batter will be almost a bit "foamy" to the touch.
Fill the muffin cups three-quarters full and bake until a toothpick inserted into the center of a cupcake comes out clean, 19-20 minutes.
Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.
Assemble the Cupcakes: Using a paring knife, cut into the center of the cupcake at a 45-degree angle about ⅛-inch from the edge and cut all the way around. Remove the cone and cut away all but the top ¼ inch, leaving a small disk of cake.
Fill the inside of each cupcake with room-temp pastry cream and top with the disk of cake. Serve at room temp.