Put the butter into the bowl of the stand mixer and cream it using the paddle attachment.
Add the confectioners’ sugar, the ground hazelnuts, and the cinnamon, and mix together well.
Add the eggs, one by one, mixing continuously until fully incorporated.
Sift in the flour, the baking powder, and the cocoa powder. Mix well, until a dough is formed.
Remove the dough from the bowl and divide the dough into three equal pieces. Shape each piece into a disk and cover in plastic wrap. Chill overnight.
Day 2 - Finish the Tart
Pastry: Preheat oven to 325 °F (160 °C).
Using one of the pieces of pastry, line the bottom and sides of the baking pan. If using a tart pan, bring the pastry all the way up to the top. If using a springform pan, bring the pastry about half way up the sides. Pour beans or rice into the bottom of the pastry, covering the surface. Bake in the preheated oven for 15 minutes. Remove from the oven and set aside.
***While the pastry bakes***
Caramel Filling: In the medium saucepan, add the sugar, water, and corn syrup. Cook over medium heat (heat setting 5 on my gas cooktop), stirring constantly, until all of the sugar is dissolved and the mixture begins to boil. Stop stirring. Don't stir anymore! (If you continue to stir, sugar crystals may form and make the caramel grainy.)
Reduce the heat to low (heat setting 3 on my gas cooktop) and continue to slowly boil until the color of the caramel changes from clear to a deep, golden amber. Remove from heat immediately! Stir in the heavy cream or crème fraiche and then add the butter. Mix thoroughly. Set aside to cool.
In the small mixing bowl, beat the eggs and then whisk in the flour until no traces of flour are visible. Pour the egg and flour mixture into the cream-caramel mixture and mix thoroughly.
Pour the beans/rice out of the pastry shell, and add the caramel mixture. Bake in the preheated oven for 15 minutes. Remove from the oven and allow to cool completely.
Chocolate Mousse: Put the chopped chocolate into the glass bowl and melt in the microwave, cooking for 30 seconds on medium heat. Stir and repeat until the chocolate is almost completely melted. Stir the remaining small bits of chocolate into the melted chocolate and set aside to cool.
When the chocolate is cool, put the whipping cream into the bowl of the stand mixer and beat it using the wire whisk attachment. The cream should have stiff peaks. Gently fold in the cooled chocolate until fully incorporated. Don't beat it or the mousse will lose volume.
Spread the chocolate mousse over the cooled caramel layer. Chill for one hour in the refrigerator. (Optional: Reserve about ¾ cup of the mousse. Put it into a plastic bag fitted with a decorating tip and pipe stars around the edges of the tart.)
Sugar Decorations: In the small sauce pan, add the sugar and corn syrup. Cook over medium heat (heat setting 5 on my gas cooktop), stirring constantly, until all of the sugar is dissolved and the mixture begins to boil. Stop stirring. Reduce the heat to low (heat setting 3 on my gas cooktop) and continue to slowly boil until the color of the caramel changes from clear to light amber. Quickly pour it onto the parchment lined baking sheet, making designs as you go. The melted sugar will begin to cool as you pour and you will get some filaments, but that's ok. Allow the sugar to cool thoroughly, then break it up into small pieces and put them on top of the tart.
Tips: If your sugar happens to burn, just pour it out into a can from your recycle bin. Add water to the pan and set it back on the burner on low heat. This will break up the burnt sugar and make clean up a lot easier.