1Heat oven to 350°F. Grease 9-inch round or 8-inch square pan with shortening or cooking spray. In small bowl, mix 1 cup flour, the baking powder, baking soda and salt; set aside.
2In large bowl, beat 1/4 cup butter and the granulated sugar with spoon until light and fluffy. Beat in egg and vanilla. Alternately add flour mixture and yogurt to butter mixture, beating well after each addition. Spread batter in pan. Arrange apple slices over batter.
3In small bowl, mix topping ingredients except butter. With pastry blender or fork, cut in 2 tablespoons butter until crumbly; sprinkle evenly over apples.
4Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes. If desired, remove from pan. Serve warm.