Sift together dry ingredients in large bowl.
Mix milk, egg and shortening, and add all at once to dry ingredients.
Mix only until moist.
Batter will be lumpy.
Fill greased muffin cups two-thirds full.
Drop one teaspoon peanut butter in center of each muffin.
Cover with batter.
Bake until brown.
Bake at 400 degrees 18 minutes