Lemon Curd

6 tablespoons unsalted butter
1 cup lemon juice
2/3 cup granulated sugar
2 large eggs
2 egg yolks
2 teaspoons fresh-grated lemon zest

In a medium size saucepan, melt the butter over low heat. Remove from the heat, and add the lemon juice. Add the sugar, eggs, and egg yolks to the lemon butter. Using an electric mixer, beat the ingredients for about 2 minutes. The mixture will look curdled but will smooth out as it cooks. Cook over medium-low heat, whisking vigorously and continuously, until the lemon curd thickens, about 8-15 minutes. Do not let boil. It is finished cooking when it is light yellow and coats the back of a soon. Remove from the heat, and stir in the lemon zest. Transfer to a bowl, and cover by laying a piece of plastic wrap directly on top of the curd. Chill in the refrigerator for at least 3 hours before using.