In a medium bowl combine flour, cinnamon and baking powder. Whisk to blend and set aside.
In a small saucepan combine butter and brown sugar. Place them over medium heat and whisk until the butter is melted and the mixture is smooth. Remove from heat and transfer to a large bowl. Let cool for about 5 minutes until no longer hot.
Add egg and vanilla and whisk shortly until combined. Gradually add the dry ingredients, whisking gently with a wooden spoon. You will end up with a soft dough. Place it in the fridge for 20-30 minutes.
Preheat oven to 360 degrees F/ 180 degrees C.
Take small balls out of the dough and press them to the bottoms and the sides of the the muffin tin cups.
Bake for about 20-25 minutes or until the cupcakes start becoming golden around the edges. They will raise and won’t be hollow any more.
Let them cool until room temperature before frosting them.
Break the chocolate into pieces and place it in a small heatproof bowl together with 3 tbs of the cream. Place the bowl over a pan of gently simmering water (double boiler). Whisk with a rubber spatula until the chocolate is melted and the mixture is smooth. Let it cool for few minutes.
Whip the cream in a large bowl using an electric mixer. Combine it with the melted chocolate: it is easier if you first fold some of the cream into the chocolate. Repeat the procedure and then fold the mixture into the remaining cream. Mix carefully until the mousse is smooth and uniform.
Use a piping bag or a small spatula to frost the cupcakes.
Store the frosted cupcakes in airtight containers in the fridge.
If you prefer your cookie cups with chocolate chips, you can add about 3-4 oz (100-120 g) chocolate chips in the dough. Add them at the very end and mix gently until absorbed.
Make sure the cream has been refrigerated at least 6-8 hours at the top rack of the fridge, before whipping it.
These cupcakes will keep 3-4 days refrigerated. If you want to prepare them in advance, you can freeze them without frosting and then frost after thawing.
If you want your cupcakes to remain hollow (like cups), after pressing the dough to the bottom of the muffin cups, place on top pieces of parchment paper and fill each cup with pie weights or dried beans. The weights will not allow the cookie dough to raise in the middle.