Lemon/Raspberry Streusel Muffins

In a large bowl, combine flour, sugar, baking powder, baking soda and salt. Combine eggs, yogurt, oil and lemon zest; mix well. Stir into dry ingredients just until moistened. Fold in raspberries. Fill greased or paper-lined muffin cups three-fourths full. For topping, combine sugar and flour. Cut in butter until mixture resembles coarse crumbs; sprinkle about 1 tablespoon over each muffin. Bake at 400° for 18-20 minutes or until muffins test done. Cool in pan 10 minutes before removing to a wire rack.