Preheat oven to 375 F (190 C).

Grease 15x10 inch baking pan and line bottom with parchment paper. Grease the paper as well.

In a boel stir together dry ingredients - flour, cinnamon, baking powder and salt.

Beat eggs with an electric mixer on high until thick. Slowly add sugar, beating on medium-high until light and fluffy for 3 minutes.

Add pumpkin and vinegar, beat until compined.

Spread batter in the prepared pan. Bake for 15 minutes, until cake springs back when touched.

Loosen edges with a knife and turn cake onto parchment paper, sprinkled with powdered sugar. Let it cool down completely.

Cut cake crosswise into 3 rectangles.

Beat heavy cream, mascarpone and powder sugar with a mixer on medium-high for 3-4 minutes until soft peaks form.

Prepare the coffee syrup:

Combine coffee and 1 tsp sugar.

Place 1 layer on a platter and brush with coffe syrup. Spread mascarpone cream on top.

Add the second layer and repeat.

Add the third layer, brush with syrup and spread mascarpone cream on top.

Spread mascarpone cream on all sides of the cake.

Drizzle melted chocolate on top and on the sides of the cake, top with chopped hazelnuts.

Refrigerate for 4-6 hours to set.