Pre heat the oven to 375 °F and lightly grease muffin tin.
In a medium bowl, combine flour, sugar, baking powder, and salt.
In a seperate bowl, whisk egg, milk, oil, and vanilla together.
Stir in the wet ingredients with the dry ingredients until just combined. Do not overmix. You want your mixture fairly thick.
Fold in frozen berries.
Note: using frozen berries prevents the colours from running through the mix.
Place about a teaspoon of jam ontop of the mixture, then add just enough muffin batter on top to cover. Sprinkle with sugar, and place it in the oven for approximately 20-25 or until centres come out clean.
Allow muffins to cool completely before removing from tin. Enjoy!