Preheat oven to 350 degrees. Line a 9x13 pan with foil and spray with cooking spray.
Cream sugar and butter in the bowl of an electric mixer fitted with a paddle attachment. Add eggs and vanilla and beat until combined. Mix in lemon juice and zest. Add baking powder, salt, and flour and mix. Stir in coconut.
Spread into prepared pan.
Bake at 350 for 23-25 minutes. Do not over bake or they will be dry and cakey. It's best to remove them from the oven when they are still a little underdone so they can finish baking while they cool. Remove from oven and cool completely before frosting.
To make the frosting: Melt butter and white chocolate together in microwave. Stir in powdered sugar and vanilla.
Stir in cream to get desired consistency (I used 1 teaspoon). The mixtured seemed separated, but still worked!
Spread a light coating evenly over the top of your bars and sprinkle with extra coconut.