Gianduia Cake

Whisk together flour, vanilla extract, baking soda, and cocoa powder

Add 3 tablespoons of chopped hazelnuts and mix until just combined

Set aside

Beat eggs and yolks until light and fluffy, then gradually add milk, beating until the mixture doubles in volume and becomes smooth

Add the reserved flour mixture and mix delicately with a wooden spoon

Grease a 25cm-diameter cake pan and line it with parchment paper, greased as well

Spread the batter evenly and bake in a preheated oven at 180°C for 30 minutes, or until a toothpick comes out clean

Let cool, then remove from pan

Prepare the filling and topping: melt chocolate in a double boiler and let it cool

In a bowl, combine water, vanilla extract, liqueur, and mix well until the vanilla dissolves

Add 1/2 cup of this mixture to the melted chocolate and stir gently until the liquid is fully incorporated into the chocolate

Divide the mixture in half and set one half aside for the topping (it will be a thick paste)

With the other half, prepare the filling: add butter and the remaining hazelnuts, and mix vigorously with a wooden spoon until it has a good consistency for spreading

Let it chill in the refrigerator for about 10 minutes

To assemble: cut a circle of parchment paper to the same size as the cake's circumference

Line one side of the paper with waxed paper and secure with tape, then place one half of the cake on top

Moisten with a little liqueur, then spread 3/4 of the chocolate topping over the filling

Place the other half of the cake on top, cut-side up, and moisten with the remaining liqueur

Spread the remaining filling around the edges and top of the cake to cover any gaps

Place the cake on a serving plate turned upside down so it doesn't touch the surface

Melt the reserved topping mixture in a double boiler until smooth

Let it cool, then slowly pour it over the center of the cake, allowing it to flow and cover the entire cake

Chill in the refrigerator for about 20 minutes or until the topping sets

Serve chilled.