Line two baking trays with parchment paper and set them aside.
In a medium bowl, combine the flour, cocoa powder, salt, and baking powder, then give them a quick whisk to blend.
In a separate large bowl, cream the softened butter with both sugars for about 2 minutes until the mixture is smooth and airy.
Add the egg yolks and vanilla, mixing until everything becomes lighter in color and fluffy.
Add the dry mixture to the bowl and mix on low just until a soft dough comes together—stop as soon as it forms to avoid overmixing.
Portion the dough into 30–35 pieces (around 1 tablespoon each) and roll them into neat, even balls.
Arrange the dough balls on the lined trays. Using a 1/4-teaspoon, press gently in the center of each one to create a small dip.
Chill the shaped dough in the fridge for at least 1 hour so they firm up before baking.
Preheat the oven to 180°C.
Once chilled, space the dough balls evenly on the baking trays and bake for 10–12 minutes. Allow them to cool completely.
Spoon 1 teaspoon of Nutella into each indentation and finish with sprinkles or any decoration you like.
