Preheat oven to 375°F. Grease muffin tins or line with paper cups.
Beat peanut butter, egg and sugar together until smooth. In three parts, add milk, mixing between additions to blend. Add flour and baking powder and mix just until flour disappears.
Spoon a heaped tablespoon of batter into each muffin cup. Place 1 teaspoon jam in the center and then cover with vatter until the cup is ¾ full.
Bake about 20 minutes, until a tester poked in the center comes out clean.