Preheat over to 350F. Pam a 9" square pan. Dust with flour and put in freezer.
Mix flour, baking powder and salt. Cream butter and ¾ cup sugar in the mixer (use the paddle) until light and fluffy. Add egg, vanilla and orange zest. Stir in yogurt and milk and mix.
Transfer batter to chilled pan. Sprinkle remaining sugar on top. I like to add some cinnamon as well. Bake 25-30 minutes or until cake tester comes out clean.
Additional Notes
You can replace ½ cup wheat flour with almond flour. It will enrich the cake and make it taste more moist. Dick is allergic to nuts so I can't do it…