HEAT oven to 375ºF. Spray muffin pan with no-stick cooking spray. Stir together flour, salt and baking powder in large bowl. Add milk, eggs, 2/3 cup sugar, peanut butter and oil to bowl. Combine ingredients with mixer on low speed, just until moistened. Do not over beat.
FILL prepared muffin cups with half of batter. Place 2 level teaspoons jam or preserves in center of each muffin. Divide remaining batter between muffin cups. Sprinkle with 1/4 cup sugar. Bake 18 to 20 minutes. Remove from oven. Cool in pan 5 minutes.