Key tip: have the eggs at room temperature.
Pour one half cup of fresh lemon juice over 3/4 cup sugar. Let steep and dissolve a bit, stirring it along.
Beat two eggs well, in a medium saucepan. Add lemon mixture, blending well. Cut one stick of butter into pieces, add to mixture.
Set saucepan (or double boiler) over (OVER, not IN)
simmering water, adding water as necessary. Stir gently and occasionally as the mixture warms up, monitor it more closely as you go along, 15 minutes or more. At some magical point it will turn from soup to custard, and you will have a very fine lemon curd indeed. (What's the clue? It will now coat your spoon, rather than slip off). Mix in a teaspoon or two of finely grated zest. Cool. Slather it onto scones, biscuits, muffins, top off your non-fat Greek yogurt, spoon into pre-made tart shells. I like it for breakfast. And lunch. And dinner.