In a bowl, combine the dry ingredients: hazelnut flour, cocoa powder, baking powder, and salt. Mix and set aside. In a second bowl, briefly beat the eggs with the sugar. Add the melted butter, vanilla extract, and hazelnut cream. Whisk until combined. Preheat the oven to 180°C (350°F). Combine the contents of the two bowls and mix well until the mixture is thick and creamy. If it's too thick, add a splash of milk. Finally, add the chocolate chips and mix with a spatula. Transfer to a square or rectangular baking pan lined with parchment paper. Bake at 180°C (350°F) for 30-35 minutes. Remove from the oven, let cool, and then divide into 12 cubes. Top each cube with a drizzle of hazelnut cream and attach the monster eyes to the brownies. All you have to do is enjoy them… Trick or treat?