Lemon curd is a lemony thickened mixture made from eggs, lemons, sugar, unsalted butter and lemon zest. Lemon curd is well-known in the U.K. where it is served with scones at afternoon tea. It can be used as a topping or a filling too.
You can find this product ready-made in most well stocked grocery stores or gourmet food stores. You can also purchase it online at Amazon.com Lemon Curd
If you don't have lemon curd you may use one of these alternatives:
1 large lemon
3/4 cup butter
1 cup sugar
Grate the lemon so that you have 1 tablespoon (peel only, no white pith).
Then squeeze the lemon; you should have about 3 tablespoons of juice.
In a double boiler over hot, not boiling, water, or in heavy 2-quart saucepan over low heat, stir lemon juice, lemon peel, butter, and sugar until the butter melts.
In a small bowl, beat eggs slightly. Add the eggs to butter mixture and cook, stirring constantly, until mixture is very thick and coats the back of a spoon well, about 15 minutes (do not boil or mixture will curdle).
Refrigerate until you are ready to use it.