1. Sift flour and baking powder together into a bowl, add sugar and mix to combine.
2. Combine eggs, milk and butter. Add egg mixture and blueberries to dry ingredients and mix until just combined.
3. Spoon mixture into six greased 1 cup / 250 ml / 8 fl oz capacity muffin tins. Sprinkle with coffee sugar crystals and bake at 200° C / 400° F / Gas 6 for 20-30 minutes or until muffins are cooked when tested with a skewer. Turn onto wire racks to cool.