Preheat the oven to 190˚C (170˚C fan oven, 375˚F, gas 5). Lightly grease a 12 cup muffin or cupcake tin. Sift the flour and Baking Powder into a bowl. Stir in the sugar and make a well in the centre.
Mix the egg, milk, melted butter and Vanilla Extract together and pour into the well, then stir to form a stiff, well-blended batter. Carefully fold in the blueberries.
Divide the batter equally between the muffin tins. Smooth the tops slightly and bake for 22-25 minutes, until risen and lightly golden. Cool for 5 minutes in the tin, then keeping the muffins in the tin, inject each one generously with Blueberry Jam using a piping bag. Leave to cool for a further 10 minutes before carefully removing from the tin and placing on a wire rack to cool.
Your muffins are now ready to serve and enjoy – delicious served warm!