Preheat your oven to 180°C (350°F) and adjust the oven rack to the middle position. Line a 12-cup muffin tin with pretty muffin wrappers.
Grate the lemons to get the zest and squeeze the juice, making sure to remove any seeds. Freshly squeezed lemon juice is essential for the best flavour.
In a bowl, beat the eggs, vegetable oil and lemon juice together.
In a separate bowl, whisk together the gluten-free flour, baking powder, and xanthan gum (if using). Add the lemon zest and sultanas to the dry ingredients and whisk to combine.
Add the dry ingredients to the wet ingredients and mix until just combined. Be careful not to overmix, as this can result in dense muffins.
Divide the batter evenly among the muffin cups. You can fill them about two-thirds full.
Bake the muffins for about 20 minutes or until a skewer inserted into the centre comes out clean. Let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
In a small bowl, whisk together the icing sugar and lemon juice until smooth. You can adjust the consistency by adding more sugar or lemon juice.
Once the muffins are completely cool, drizzle them with the lemon drizzle. You can also sprinkle a bit of extra lemon zest on top for added flair.