In a medium bowl, sift the flour with the baking powder and salt. Mix with a spoon and set aside. Separately, in a large bowl, add the sugar with the cocoa powder and oil. Beat with an electric mixer or hand whisk for 1 minute until smooth and shiny.
Add in the eggs one at a time, beating after each addition and then add the vanilla extract. Beat for a few seconds more until all the ingredients are perfectly integrated.
Add the flour mixture in two separate additions and integrate with a rubber spatula until you get a very smooth batter. It is important to not over beat the batter.
Cover the bowl with plastic wrap and refrigerate for 4 hours or preferably overnight for better consistency and flavor.
Once it has cooled, preheat the oven to 180° C (350° F). Place baking paper on two large trays and place the powdered sugar in a small bowl.
Using a small ice cream scoop or spoon, portion the dough into 20 small balls about the size of 1 tablespoon and then roll them in the powdered sugar until well coated. Place them on the baking sheets, at least 5 cm apart from each other. It is important to only cover the dough balls that are going to be baked right away. The rest of the dough balls should be refrigerated and dipped in powdered sugar just before baking.
Bake the cookies for 10-12 minutes until firm and lightly browned on the edges but not quite in the center. take out of the oven and let them cool down on the baking sheets for 10 minutes. Then put them on a wire rack to cool down completely.