In large mixing bowl beat together butter, oil, cocoa and 2 cups sugar.
Add eggs, mixing well, then stir in vanilla.
In medium mixing bowl combine flour, baking powder and salt.
Stir into cocoa batter.
Refrigerate several hours or overnight.
When ready to make, preheat oven to 350°F.
Place each of the two sugars left into separate bowls.
Drop rounded teaspoonfuls of dough into granulated sugar, roll to coat, then roll in powdered sugar. Place on greased cookie sheet 2 inches apart.
Bake 10 to 12 minutes until cookies are puffed but slightly firm at edges.
Note: Rolling cookies in granulated sugar first prevents dough from absorbing powdered sugar. This step can be omitted, but creates more of a contrast between white sugar and dark brown cookie.