Mix together eggs, sugar, vegetable oil and vanilla extract for a few minutes.
Combine the flour with cocoa, baking powder and salt. Sift into the wet ingredients and mix well until fully incorporated. Don't whip, mix gently!
Leave the dough into the freezer for at least an hour (you may leave it overnight). Divide the dough into 35-40 g balls, and roll them through powdered sugar.
Arrange them on parchment paper, leaving 4-5 cm in between them. Bake at 180°C for 10-12 minutes. The cookies will be tender in the beginning, they become steadier after they cool down. Store in a tightly closed container.