To Make the Cake:

Generously oil the cups of a 12-cup muffin pan; set aside. Oil a wire rack; set aside for cooling the cupcakes.

Preheat oven to 350°F.

In the bowl of your mixer, beat the egg yolks and sugar on high for about 5 minutes, scraping sides of bowl if needed.

Slowly pour in hot water over a 90-seconds span, beating on high speed the entire time. Allow batter to rest and cool for 2 minutes.

Gradually sift in the flour and salt mix on low speed until smooth.

Add vanilla and beat on low speed until incorporated; and set aside.

Using a clean mixing bowl, beat egg whites on high speed until stiff peaks form, about 2 minutes using a high-powdered mixer.

Using a rubber spatula, fold the whipped egg whites, one-third at a time, into the batter that you set aside. (Be careful not to over mix.)

Distribute evenly among the prepared muffin tins and smooth out the tops. (Do not tap on countertop as this pops the air bubbles, which is vital to sponge-type cakes.)

Bake for about 17 minutes or until the cake springs back up when pressed with finger tips and a toothpick comes out clean when inserted in the center of one of the cupcakes.

Allow the cupcakes to cool in pan for 10 minutes. At this point, do not place the pan on a wire rack. (This allows steam to form which softens the crust.)

Loosen cupcakes from the pan and transfer to the prepared wire rack; allow to cool completely.

To Make the Filling:

While the cupcakes cool, in the clean bowl of your mixer, cream the butter until smooth scraping bowl as needed.

Add the cream and beat on high speed until thoroughly combined, scraping bowl as needed.

Sift in confectioners' sugar and beat until light and fluffy, about 5 minutes.

Add the vanilla and beat the mixture on low speed until thoroughly combined.

To Fill the Cakes:

Using a straw (or ice pick or wooden skewer moved about to create a straw-sized hole), poke a hole in the bottom of each cupcake, if you do not plan on frosting the tops. Otherwise, poke a hole in the center of the top each cupcake.

Fill a pastry bag or piping device with some filling and pipe enough into each of the holes until you notice the cupcake becoming slightly plump. Don’t overfill them or they will burst.

If desired, frost the top with your favorite buttercream or marshmallow frosting.

Serve immediately and freeze leftovers, uncovered, on a sheet of parchment paper. Then once frozen store and freeze in freezer bags. Remove from bag and defrost at room temperature.