Preheat oven to 350°F. Grease a 12-cup muffin tin or line with paper liners.

In a large bowl, whisk together flour, sugars, baking soda, baking powder, and salt.

In a separate bowl, beat egg. Add buttermilk, milk, peanut butter, oil, and vanilla; mix well.

Pour wet ingredients into dry ingredients. Fold gently until just combined; do not overmix.

Spoon about one-third of batter into each muffin cup. Add a small spoonful of jelly in the center. Cover with remaining batter.

Bake for 20-24 minutes until muffins are golden and spring back when lightly pressed.

Remove muffins from oven, allow to cool in tin for 5 minutes, then transfer to wire rack to cool completely.