PREPARATION:

1. Preheat oven to 375°F. Melt 1/4 cup butter in 8-inch square baking pan in oven. Add 1/2 cup brown sugar, cinnamon and nutmeg; mix well. Arrange apples over brown sugar mixture in bottom of pan; sprinkle with lemon juice.
2. Combine flour, granulated sugar, remaining 1/4 cup brown sugar and salt in large bowl. Cut in remaining 3 tablespoons butter with pastry blender or 2 knives until mixture resembles coarse crumbs.
3. Add milk and vanilla; beat with electric mixer at low speed until dry ingredients are moistened. Continue beating 2 minutes at medium speed. Blend in egg yolk.
4. Beat egg white in small bowl with electric mixer at high speed until stiff peaks form; gently fold into batter. Pour over apples in pan.
5. Bake 35 minutes or until toothpick inserted into center comes out clean. Cool in pan on wire rack 5 minutes. Loosen edges and invert onto serving plate. Let stand 1 minute before removing pan. Serve warm.