Slice the lemons as thinly as possible.
Place the sugar and water into a pot over a medium heat and stir until the sugar dissolves.
Add the lemon slices to the pot and bring to the boil. Turn down to simmer and leave for 15 minutes.
Lift the lemon slices out of the syrup with a fork and leave on a wire rack set over a piece of baking paper to dry and cool.
Keep the resulting lemon syrup in the pot for brushing onto the cakes.