Add the egg yolk, sugar, and the lemon juice to medium sized saucepan.
Heat on medium high while whisking, gently.
Bring the mixture to a boil while continuing to whisk.
You will be whisking for about 10-20 minutes, until the curd mixture is thick enough to coat the back of a spoon.
Add the butter in one chunk at a time. Whisk slowly while the butter melts.
Remove from the heat and add in the lemon zest. The lemon curd will continue to thicken as it cools.
Store in an air tight container, up to 3 weeks in the fridge.
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RECIPE TIPS
Pro-tips:
Whisk constantly: The key to making perfect lemon curd is stirring constantly. This keeps the fruit curd from sticking to bottom of the pan and burning and allows the mixture to heat evenly and thoroughly as it thickens.
Back of the spoon test: To check for doneness, remove the pan from the heat (actually move it off the burner) then use the back of a spoon to dip in. If the curd coats the back of the spoon then it is done. I try to get mine somewhere in between the consistency of thicker than maple syrup but thinner than honey. It will continue to thicken after it cools so don't worry if it seems a little thin.
If it's not thick enough return the pan to the burner and continue to whisk and heat. Usually, about 10 minutes of heating and whisking is sufficient to get the right amount of thickness in your lemon curd.
Serve with: Pancakes, Scones, French Crepes, Pavlova. Also, use as a filling for cupcakes or slather between layers of white cake. This lemon curd makes amazing lemon bars, and lemon tarts. Recipe VariationsFruit curd, and mainly citrus curd, can be made with almost any acidic fruit.The recipe can be used to make Lime Curd, Grapefruit Curd, Orange Curd, and even Passion Fruit Curd, or Pineapple curd. Pineapple curd will need to be thickened with a cornstarch slurry.