Make the Crepe Batter: In a large mixing bowl, whisk together flour, cocoa powder, sugar, and salt. Add the eggs and gradually pour in the milk while mixing continuously until smooth. Stir in the melted butter. Let the batter rest for 30 minutes.
Cook the Crepes: Heat a non-stick skillet over medium heat. Lightly grease with a bit of butter if necessary. Pour about 1/4 cup of crepe batter into the pan and swirl to cover the bottom evenly. Cook for 1-2 minutes until the edges start to lift, then flip and cook for an additional 30 seconds. Repeat with the remaining batter, stacking the cooked crepes on a plate.
Prepare the Whipped Cream: In a large bowl, whip the heavy cream until soft peaks form. Gently fold in 1/2 cup of chocolate hazelnut spread until well combined.
Assemble the Cake: On a serving platter, place one crepe and spread a thin layer of the hazelnut cream mixture on top. Add another crepe and repeat the process until all crepes are stacked, finishing with a crepe on top.
Chill the Cake: Cover the assembled crepe cake with plastic wrap and refrigerate for at least 2 hours or overnight for the flavors to meld.
Serve: Before serving, sprinkle the top with toasted hazelnuts and dust with powdered sugar for added sweetness. Slice into wedges and enjoy!