Step 1: Preheat your oven to 200°C (392°F) and line a muffin tin with paper liners.
Step 2: In a mixing bowl, add your zested lemon, lime and sugar. Use your fingertips to rub the ingredients together to release their natural citrus oils.
Step 3: Add the sunflower oil, melted butter, whole milk, lemon extract and egg. Mix until smooth.
Step 4: Add the self-raising flour and mix until just combined. Don't overmix!
Step 5: Space out your muffin cases in the pan, don't overcrowd. This allows them to rise properly.
Step 6: Fill the muffin cups about 2/3 full with the batter.
Step 7: Top with pearl sugar, then swirl into the top of the muffin.
Step 8: Add more pearl sugar, focusing on the middle. As the cake rises, the sugar will move outwards.
Step 9: Change oven temperature to 180°C (350°F) and bake for 20 minutes or until a toothpick comes out clean.
Step 10: Remove from oven and let cool in the tin for a few minutes, then transfer to a wire rack.
Step 11: After cooling for 20 minutes, fill a piping bag with lemon curd. Pierce a small hole into the top of each muffin and fill with lemon curd.
Step 12: For the glaze, combine icing sugar and water until you have a thick paste.
Step 13: Fill a piping bag with icing and pipe a circle on top of the lemon curd.