Sugar Cookie

Whisk flours, baking powder, and salt in a bowl. In another bowl, beat butter and sugar with a hand mixer until light and fluffy; add egg whites and vanilla, and beat until just combined. Gradually stir flour mixture into butter mixture until combined. Form dough into a log, wrap tightly in waxed paper and refrigerate at least 3 hours. For plain sugar cookies, heat oven to 350°F. Cut dough in half; roll out both halves to an even 1/4-inch thickness. Cut out 40 cookies using a 2-inch cutter. Coat 2 cookie sheets with cooking spray; place cookies on sheets 1 inch apart and bake until firm, 6 to 8 minutes.