Preheat the oven to 325 degrees Fahrenheit. Grease three 8-inch round cake pans and line the bottoms with parchment paper. Set aside.

In a large bowl, stir together the flour, sugar, cocoa powder, baking soda, and salt. Set aside.

In the bowl of an electric mixer fitted with with whisk attachment, beat together the eggs and sour cream until smooth and creamy. Add the vegetable oil, hazelnut liqueur, and vanilla extract and mix until combined.

Switch to the paddle attachment, and add the flour mixture to the egg mixture and mix at low speed until coarsely combined (the batter will be thick and chunky, and that's okay). With the mixer running at low speed, add the coffee in a steady stream and mix until it is *just* incorporated and a smooth batter forms, stopping to scrape down the sides and bottom of the bowl with a rubber spatula as-needed.

Evenly distribute the batter between the three cake pans and place in the oven. Bake until a toothpick insert inserted the center comes out clean, about 20 to 25 minutes minutes. Set tray on a wire rack to cool for 10 minutes, then unmold the cakes onto the wire rack and allow to cool to room temperature while you prepare the rest of the recipe.

Preheat the oven to 350 degrees Fahrenheit. Evenly distribute the hazelnuts in one layer on a large lipped baking sheet. Place in the oven and bake until fragrant and any exposed pale parts of the hazelnut are lightly golden, about 10 to 13 minutes. Remove and allow to cool for 4 minutes, then take 1 cup of the hazelnuts and set it aside to use for decorating the cake at the end.

Dump the remaining hazelnuts onto a clean kitchen towel. Rub the hazelnuts in the towel to get their skins off. Leaving the skins behind (the skins can be composted), place the skinned hazelnuts in the bowl of a food processor. Add the salt and process at high speed until a smooth, oily butter forms, about 2 to 3 minutes (if you're using a high-powered blender, it will take longer). Makes about 1 and 1/4 cups toasted hazelnut butter.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter until smooth, then add toasted hazelnut butter in bowl of stand mixer until creamy and smooth. Add the powdered sugar, hazelnut liqueur, heavy cream, and salt and mix at medium high speed until fluffy and airy in texture, about 3-4 minutes.

Use a long knife to cut the domes off the cake layers so that they are flat on top (enjoy the domes as a snack!) Place the first layer on the serving plate and frost the top of it with the buttercream using an icing spatula or rubber spatula. Place the second layer of cake on top and repeat the icing. Place the third and final cake layer on top and ice the top of the cake and a thin layer of icing on the sides. Place the cake in the freezer for 15 minutes to let the icing harden (this will keep the crumbs of the cake from mixing into the frosting as much). Remove the cake from the freezer and continue frosting the cake until you no longer see the cake showing through the frosting. (If you want to have the stars of buttercream on the top of the cake, you'll need to reserve about 3/4 cup of buttercream). If you'd like, you can mix a couple tablespoons of icing in a bowl with a tablespoon of hazelnut butter, and dab it on the cake in a few places and then smear it smooth with the spatula. This will create some fun variation in color.

Place the cake in the refrigerator for 10 minutes while you create the chocolate glaze (follow recipe below). Remove the cake from the refrigerator and drizzle the glaze on the cake, using a clean icing spatula or rubber spatula to gently smooth out the glaze on the top of the cake and allow some snazzy drips to form along the sides. When you're happy with the appearance, put the cake in the refrigerator for 30 minutes to allow the glaze to firm up a bit.

Use a pastry bag fitted with a star tip and filled with the remaining buttercream to pipe little star "dollops" on top of the cake in a circle around the edge, trying to evenly space them apart from each other. Place a toasted hazelnut on each one. Serve and enjoy! Will keep covered in an airtight container for several days.

Melt the butter in a small saucepan over low heat. Add the chocolate chips and stir constantly until melted. Remove from heat and use immediately.