Preheat oven to 350F, grease, and line the bottom of 4-6" pans with parchment paper. Set aside.

In a medium bowl, sift the flour, baking powder, baking soda, then hazelnut powder, and mix with a fork to combine. Set aside.

In a large measuring cup, mix the milk, sour cream, vanilla, and Frangelico and mix to combine.

Place the butter and sugar in a bowl of a standing mixer and beat using the paddle attachment on medium speed until light and fluffy. 4-5 minutes.

Scrape the bottom and sides of the bowl then increase speed to medium-high and add the eggs one at a time, waiting for each egg to be completely incorporated before adding the next.

Add the flour mixture in 3 additions alternating with the liquid. Starting and ending with the flour.

Once you added the last part of the flour, turn the mixer off add the chopped hazelnuts and chocolate chips, and use a rubber spatula to combine it all.

Dived the batter between the greased pans and bake for 28-30 minutes or until a toothpick comes out clean from the center of the cake.

Remove cakes from the oven and allow to cool before removing from the pan.

Use a large knife to roughly chopped the hazelnuts, each nut should be sliced once or twice.

Place the nuts in a medium-sized pan, pour over the heavy cream and milk then bring to a boil. Once boiling, turn the stove off, cover the pan and let cool to room temperature.

Run the hazelnut milk through a sieve and measure 1 cup and place it back in the pan and bring to a simmer. Discard the nuts or enjoy them as a treat.

In a medium bowl, mix together the egg yolk, sugar, and cornstarch. Place the bowl next to the stove and have a large sieve ready to be used.

Once the hazelnut milk is simmering, turn the stove off then slowly drizzle about 1/2 cup of the milk into the egg yolk mixture while constantly stirring.

Pour the egg yolk mixture into the remaining milk and cook on medium while constantly stirring until the mixture has thickened and large bubbles are coming to the surface, about 3 minutes.

Run the curd through the sieve into a medium bowl, cover with plastic wrap, and allow it to cook down to room temperature.

In a bowl of a standing mixer, beat the butter on high for 30 seconds.

Scrape the bottom and sides of the bowl then add the now room temperature hazelnut curd. Keep mixing until the curd is fully incorporated and thick.

In a medium bowl, place the chocolate and vegetable shortening. Warm in the microwave using 30 seconds increments until completely melted.

In a medium saucepan, pour the milk, Frangelico and granulate sugar then cook on medium until the sugar has fully dissolved and the liquid came to a boil. Avoid overcooking it or the Frangelico will completely evaporate leaving you with less syrup.

Place one layer of cake on top of a cake board or your serving plate. Use a pastry brush to soak 1/4 cup of the simple syrup.

Using an offset spatula, evenly spread 1/4-1/3 cup of the buttercream. If you decide to fill the cake with some chocolate as well, after spreading the buttercream fill a pastry bag fitted with a round tip (I used Wilton #8) then pipe a border along the edges of the cake and fill it with the chocolate filling (make sure it is at room temperature).

Repeat step 1 with the remaining of the cakes then use the remaining of the buttercream to coat and frost the cake, then drizzle with the melted chocolate. (make sure it is at room temperature)