1. In a large mixing bowl, add egg, vanilla, oil, and brown sugar. Beat until well combined.
2. Sift, and add cocoa and baking powder in it.
3. Add flour and mix it well.
4. Preheat oven to 180 degree C or 350 degree F.
5. Clump mixture, and roll it into balls.
6. Line a baking sheet with parchment paper. Place the balls on baking sheet and flatten it with a fork.
7. Place baking sheet in oven, and bake for about 12-15 minutes. Remove from oven and let it cool for 5-10 minutes.
8. Transfer it to a plate, and serve cookies warm with a cup of milk.