Preheat your oven to 350°F (175°C) and prepare two round 9-inch cake pans by greasing them with butter or non-stick spray and dusting with flour.

In a spacious mixing bowl, whisk together all-purpose flour, cocoa powder, baking powder, baking soda, and salt.

In another bowl, combine granulated sugar, melted unsalted butter, vegetable oil, eggs, Frangelico, and warm coffee and whisk until smooth.

Gradually pour the wet ingredients into the bowl of dry ingredients while gently folding them together until smooth.

Evenly divide the batter between the prepared cake pans and bake for approximately 28 minutes or until a toothpick comes out clean.

Allow the layers to cool in the pans for around 10 minutes before transferring them to a wire rack to cool completely.

In a saucepan over low heat, combine Nutella and heavy cream, stirring until smooth, then let cool and refrigerate until thickened.

In a large mixing bowl, beat unsalted butter until creamy, then add powdered sugar, cocoa powder, Nutella, vanilla extract, and salt, mixing until fluffy.

To assemble, place one cooled cake layer on a stand, pipe a dam of buttercream, fill with ganache, and repeat with the second layer.

Refrigerate the assembled cake for at least 30 minutes before serving, garnishing with chopped hazelnuts if desired.