In a medium mixing bowl, whisk together flour, brown sugar, soda, baking powder and salt.
Add melted butter and mix until dough forms.
Press the dough into the bottoms of cups in the pan, dividing equally. Set aside.
!to make the filling:
Place all filling ingredients in a large mixing bowl of a stand mixer and mix until all combined.
Pour over crust.
Bake mini cheesecakes for 15 minutes. They will puff up but go down as they cool. Cool in the pan completely.
!to make the mousse:
Place chocolate and water in double boiler. Melt completely. Whisk till smooth.
Transfer the melted chocolate into a large mixing bowl of a stand mixer. Whip for 4 to 5 minutes. In the meantime, fill a very large pot or mixing bowl with a cold water. Fill it only ¼ of the way up.
Turn of the mixer and place the mixer bowl in the cold water bath. Make sure no water gets inside.
Leave it for 5 minutes.
Transfer the mixer bowl back into the mixer base. Whip the chocolate mousse until lighter in color and stiff like frosting. Add vanilla slowly and continue whipping.
Chill the mousse thoroughly (at least 2 hours). It will harden up. To soften it up to a spreadable consistency, place back in the mixer bowl and whip adding the milk.
Decorate the mini cheesecakes. Top with chopped hazelnuts.