Ham and Cheese Muffins

2 cups self-rising flour

1/2 teaspoon baking soda

1 cup milk

1/2 cup mayonnaise

1/2 cup finely chopped, fully cooked ham

1/2 cup shredded cheddar cheese

shredded cheese (optional)

1  note: As a substitute for each cup of self-rising flour, place 1 1/2 teaspoons baking powder and 1/2 teaspoon salt in a measuring cup.
2  Add enough all-purpose flour to equal 1 cup.
3  In a large bowl, combine flour and baking soda.
4  Combine remaining ingredients; stir into dry ingredients just until moistened.
5  Fill greased or paper-lined muffin cups two-thirds full.
6  Bake at 425 degrees (218 C) for 16 to 18 minutes or until muffins test done.
7  Sprinkle with shredded cheese while still hot if desired.