Beat the egg yolks on high speed for about 3 minutes until pale and thick.
Gradually add in brown sugar till combined, then set aside.
Heat 1 cup of the whipping cream and the whiskey over medium heat till the mixture is hot, but not boiling. You may be able to see steam rising from the surface of the liquid.
Stir some of the hot mixture into the egg yolks, then pour the egg yolk mixture back into the pot.
Heat over low, stirring constantly.
When mixture thickens, add in dulce de leche and continue stirring until smooth and combined.
Remove from heat, cover, and refrigerate for 2-3 hours.
When ready to fill the "pots", beat the second 1 cup of whipping cream until whipped cream is formed.
Fold the refrigerated caramel mix into whipped cream, until well combined.
Pour mousse into a pastry bag or large Ziplock bag, cutting off the bottom corner, and pipe mousse into the opening of each brownie.
Add festive decor and enjoy! Keep refrigerated.