This is a recipe I use for lemon curd. It is Rose Levy Beranbaum's recipe, author of The Cake Bible. It's posted on one of her sites for a lemon bar recipe that is oh so good..
2 tsp finely grated lemon zest
4 large egg yolks
3/4 cup sugar
3 fluid oz. of freshly squeezed lemon juice (about 2 1/2 lemons)
4 tbsp unsalted butter (softened or cut into pieces)
pinch of salt
(directions from her site)
In a heavy non-reactive saucepan, beat the yolks and sugar until well blended. Stir in the lemon juice, butter and salt. Cook over medium-low heat, stirring constantly (be sure to scrape the sides of the pan), until thickened and resembling hollandaise sauce, which thickly coats a wooden spoon but is still liquid enough to pour. The mixture will change from translucent to opaque and begin to take on a yellow color on the back of a wooden spoon. It must not be allowed to come to a boil or it will curdle. Whenever steam appears, remove the pan briefly from the heat, stirring constantly, to keep the mixture from boiling. When the curd has thickened, pour it at once into a strainer. Press with the back of a spoon until only the coarse residue remains. Discard the residue (or enjoy it as a treat-it tastes great). Stir gently to mix in the zest sitting in the bowl.