1. Heat oven to 350 degrees F. Coat an 8-inch square baking pan with cooking spray. Beat butter and sugar until light and fluffy. Beat in eggs, egg whites, and vanilla until well-combined.
2. In food processor, pulse apricots and flour until finely chopped. Pulse in baking powder, then wafer crumbs. Stir into egg mixture until just combined.
3. Pour batter into pan and bake 40 minutes. Cut into small squares. Sprinkle with powdered sugar.