Preheat oven to 350°.
Lightly spoon flour into dry measuring cups, and level with a knife. Combine flour, sugar, and salt in a bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Combine 1/3 cup flour mixture and candy bar for topping; set aside.
Stir baking powder and baking soda into remaining flour mixture in bowl; add yogurt, milk, rind, vanilla, and egg whites. Beat at medium speed of a mixer until blended. Spoon batter into an 8-inch round cake pan coated with cooking spray. Drop marmalade by teaspoonfuls onto batter; swirl together using the tip of a knife. Sprinkle topping over batter. Bake at 350° for 35 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack.