Place the sugar and lemon zest in a medium heat proof bowl. Use your fingers to rub the lime zest into the sugar. Set the bowl over a small saucepan 1/4 filled with water over a low-medium heat. Ensure the water won’t touch the bowl.

Add the remaining ingredients and whisk to combine. It will take a few minutes for them to come together. Once they do, continue whisking for 5-10 minutes, or until the curd has thickened and coats the back of a spoon. As soon as it does, remove it from the heat. If you’re cautious, you can plunge the bowl base into an ice or cold water bath to stop the curd from cooking.

Cover the curd with plastic wrap, flush to the curd itself so it doesn't develop a skin. Place in the fridge and allow to cool completely (if you're not using it straight away) before decanting into a clean, airtight container. Use it within a week or freeze it to preserve it for longer.