For the Cake:

1. Heat your oven to 350°F, grease and flour a 6-inch cake pan
2. In a small bowl combine the flour, cocoa powder, baking powder, salt and baking soda.
3. In the bowl of your stand mixer fitted with the paddle attachment add the butter and sugar and mix on medium speed until light and airy, about 2-3 minutes.
4. Beat in the egg and vanilla extract.
5. Mix in half the dry ingredients, then the milk and the rest of the dry ingredients. Scraping down the sides of the bowl as needed while mixing.
6. Pour the batter into the prepared cake pan and bake for 16-18 minutes or until a toothpick inserted in the center of the cake comes out clean.
7. Let the cake cool completely before breaking into small pieces. The cake can be made ahead of time.

For the Whipped Cream and Nutella Mousse:

1. In the bowl of your stand mixer fitted with the whisk attachment add the heavy cream, whiskey and hazelnut liqueur and beat on medium-high speed until the heavy cream forms stiff peaks. Be sure not to over beat the whipped cream.
2. Remove about 1/4 of the whipped cream and save to top the parfaits.
3. Add the Nutella to the bowl and gently fold in to make the mousse.

To Assemble the Parfaits:

1. Fill a parfait glass or mason jar 1/4 of the way with cake, then spoon 2 tablespoons of mousse, a few chopped hazelnuts and repeat until the glass is full.
2. Top with whipped cream and chopped hazelnuts.