HEAT oven to 400 degrees F. Spray a 12-cup muffin pan with a no-stick cooking spray or line with paper cups.
STIR together flour, sugar, baking powder and salt in medium bowl. Combine egg, milk and oil in small bowl. Add liquids to flour mixture, stirring just until dry ingredients are moistened. Divide batter evenly among cups.
COMBINE sugar, flour, peanut butter and salt in small bowl, mixing with fork until crumbly. Divide topping over muffins. Lightly stir into muffin with knife.
BAKE 18 to 23 minutes or until golden brown. Cool in pan on rack 5 minutes. Remove from pan to rack to cool completely.