Preheat the oven: Start by preheating your oven to 180°C (350°F). This ensures that your cake bakes evenly.
Prepare the cake pan: Grease and flour a round cake pan (about 9 inches) or line it with parchment paper to prevent sticking.
Cream the butter and sugar: In a large mixing bowl, beat the butter and sugar together with a mixer until the mixture is light and fluffy, about 3-5 minutes.
Add eggs: Crack the eggs into the bowl one at a time, mixing well after each addition until fully incorporated.
Combine dry ingredients: In a separate bowl, sift together flour, baking cocoa, and salt.
Mix the dry and wet: Gradually add the dry mixture into the wet mixture, folding gently until just combined.
Fold in ground hazelnuts: Carefully fold in the ground hazelnuts, making sure they are evenly distributed within the batter.
Bake: Pour the batter into the prepared cake pan and smooth out the top. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
Cool: Remove from the oven and allow the cake to cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.