Preheat oven to 350°. In a large bowl, whisk flour, sugar, baking powder and salt. In another bowl, whisk egg, milk and peanut butter until smooth; stir into flour mixture just until combined. Pour into a greased 8x4-in. loaf pan. , Bake until a toothpick inserted in the center comes out clean, 50-60 minutes. Cool for 10 minutes before removing from pan to a wire rack. If desired, serve with jelly.