1. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 3/4 cup powdered sugar, cocoa, baking powder, and salt in a medium bowl; stir with a whisk. Combine oil and chocolate in a small saucepan over low heat; cook until chocolate melts, stirring constantly. Add espresso granules to pan; stir until blended. Remove from heat. Pour chocolate mixture into a large bowl; cool 5 minutes. Stir in brown sugar, syrup, and vanilla. Add egg whites, stirring with a whisk. Add flour mixture to egg mixture, stirring gently just until combined. Cover; chill at least 2 hours or overnight.
2. Preheat oven to 350°.
3. Roll dough into 1-inch balls. Dredge balls in remaining 1/2 cup powdered sugar; place balls 2 inches apart on 2 baking sheets lined with parchment paper. Bake at 350° for 10 minutes or until tops are cracked and almost set. Cool cookies on pan 2 minutes or until set; remove from pan. Cool cookies on a wire rack.