Make the cake: Preheat the oven to 350°F. Line a 18" x 13" baking pan with parchment paper, and spray with nonstick cooking spray. Set aside.

Measure the chocolate chips into a medium-sized glass bowl. Pour the coffee on top of the chocolate, stirring with a rubber spatula until the chocolate is completely melted. (If it doesn't melt completely, pop it into the microwave for 20 seconds or so, then stir until smooth.) Add the vanilla extract to the chocolate mixture, and set aside to cool.

After the chocolate mixture is together, separate the eggs into two large glass bowls. Set the bowl with the egg whites aside for the time being.

Add the granulated sugar into the bowl with the egg yolks. Using a hand mixture, cream the two together until the mixture is a light yellow and fluffy. (This should take a few minutes.)

Once the chocolate has completely cooled, add to the egg yolk and sugar mixture, using the hand mixer to incorporate it into the ingredients. Set aside.

If you don't have two sets of beaters for your hand mixer, wash the beaters thoroughly now, then dry.

Using the hand mixer on a medium speed, whip the egg whites thoroughly until they form soft peaks.

Scoop the egg whites from their bowl into the chocolate/egg yolk/sugar mixture, and gently fold the whites into the mixture until just combined. Be careful during this step, as you don't want to overmix or deflate the egg whites.

Pour the batter on top of the parchment paper-lined baking sheet, spreading the mixture evenly. Transfer the baking sheet to the preheated oven, and bake for 20-25 minutes (depending on your oven).

Once the cake is baked through and an inserted toothpick comes out clean, remove the cake from the oven, and let cool for 10 minutes.

Remove the cake from the baking sheet using the parchment paper, and continue to cool on a cooling rack until the cake comes to room temperature.

Make the Mini Stacked Ice Cream Birthday Cakes: Using a 2" biscuit/cookie cutter, cut 20 rounds into the cooled cake.

Spread five rounds evenly on a long plate.

Using a cookie scoop, dollop about one tablespoon of softened ice cream on top of each cake round. Smooth with a knife, then top with another tablespoon of the softened ice cream. Repeat until you've used four rounds in each mini ice cream cake.

Wrap the individual cakes in plastic wrap, sealing tightly and transfer them to the freezer. Allow them at least an hour to set, though the longer they are in the freezer, the better.

When ready for the Mini Stacked Ice Cream Birthday Cakes, serve cold, topped with hot fudge and various other toppings of your choosing, and enjoy!