1. Preheat oven to 350.

2. Coat an 8-inch round cake pan with cooking spray; line bottom of pan with wax paper. Coat wax paper with cooking spray; dust with 2 teaspoons flour. Set aside.

3. Lightly spoon 1 cup flour into a dry measuring cup; level with a knife. Sift 1 cup flour and next 5 ingredients (through salt) into a bowl. Place sugar and butter in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add egg whites, 1 at a time, beating well after each addition. Add yogurt, vanilla and egg, beating until blended. Gradually add flour, beating until combined. Pour batter into prepared pan; sharply tap dish once on counter to remove air bubbles. Bake at 350 for 35 minutes or until toothpick comes out clean. Remove from oven; cool 10 minutes in a pan. Place a plate upside down on top of cake; invert cake onto plate. Carefully peel off wax paper.

4. Combine milk and chocolate in a small microwave-safe bowl. Microwave at HIGH for 30 seconds or until smooth. Cool slightly; drizzle over cake. Let glaze set; sprinkle with powdered sugar.