Mix flour, baking powder, salt, cocoa and vanilla.
Beat softened butter with sugar until light and fluffy. Add egg, beat.
Combine with dry ingredients, mix until smooth. Place in refrigerator for 1 hour.
Put on a baking sheet covered with parchment, at a small distance from each other or in a silicone mold. Bake at 180 degrees for about 7-10 minutes, carefully, do not overdry.