Linda Carucci's Lemon Curd

1. 2 to 3 Eureka lemons or 4 to 6 Meyer lemons
2. 4 whole eggs
3. 2 egg yolks
4. 1 cup sugar
5. 4 tablespoons unsalted butter (preferably organic), cut into 8 pieces
6. 1 teaspoon vanilla (preferably Tahitian)

Grate zest of 1 large Eureka or 2 Meyer lemons, using a Microplane zester, or use a citrus zester or vegetable peeler and chop zest finely. Either way, be sure to avoid the bitter white pith. Cover zest to keep it from drying out. Have ready a bowl large enough to hold 2 cups of lemon curd. Set a medium strainer over it. Squeeze enough lemons to yield 1/2 cup juice. Whisk together eggs, egg yolks, lemon juice and sugar in top of a double boiler. Add butter. Bring about 1 inch of water to a simmer in bottom part of double boiler. Set top over but not touching the water and whisk constantly until mixture thickens, which will take about 8 minutes. Do not try to speed up the procedure by increasing heat, or you will scramble the eggs. As soon as mixture thickens, remove from heat and pour it through the strainer into the bowl. Stir in reserved lemon zest and vanilla. Press a piece of wax paper directly on the surface of the curd while it cools. Cover tightly and refrigerate for up to 3 days until ready to serve.