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