Stir together first 4 ingredients in a large bowl; make a well in center of mixture.
Stir together egg, milk, and oil until blended. Add to dry ingredients, stirring just until moistened. Spoon batter into lightly greased muffin pans, filling two-thirds full.
Bake at 400° for 18 to 20 minutes. Remove from pans immediately.
Apple Muffins: Add 3/4 cup peeled, chopped apple; 1/4 teaspoon ground cinnamon; and 1/4 teaspoon ground nutmeg to dry ingredients, and proceed as directed.
Blueberry Muffins: Fold 3/4 cup fresh or frozen blueberries, unthawed, into batter, and proceed as directed.
Date-Nut Muffins: Fold 1/2 cup chopped dates and 1/2 cup chopped pecans into batter, and proceed as directed.