Preheat oven to 375°F (190°C) and line a muffin tin with paper liners.
In a bowl, whisk flour, sugar, baking powder, and salt.
In another bowl, mix eggs, peanut butter, oil, milk, and vanilla extract until smooth.
Pour wet ingredients into dry ingredients and stir until just combined.
Fill each muffin cup halfway with batter.
Add 1 teaspoon jelly to the center of each muffin.
Top with remaining batter until cups are ¾ full.
Sprinkle chopped peanuts on top if using.
Bake for 18–20 minutes until golden and set.
Cool in pan for 5 minutes before transferring to a wire rack.