Preheat oven to 350°F Spray an 8-inch square metal pan with cooking spray.
To make brownies: In a bowl, combine sugar, oil, egg, and vanilla until well mixed. Add cocoa; mix well. Add flour, baking powder, yogurt, and chocolate chips, mixing just until combined and smooth. Don’t overmix.
Pour batter into pan; bake in centre of oven for 15 to 20 minutes just until set. Do not overbake. Cool.
To make icing: In a blender or food processor, blend icing ingredients until smooth. Spread over brownie batch. Cut into squares.