Zest all of the lemons and set aside. Juice the zested lemons (should have 1/2 cup of juice) and strain the juice. In a small mixing bowl, whisk the eggs and yolks until smooth. Stir in the zest and lemon juice.
Pour the mixture into a nonreactive saucepan. Bring to a simmer over medium heat. Reduce the heat to low and continue to cook, stirring constantly with a wooden spoon, until the mixture thickens and coats the back of a spoon. Remove from the heat and transfer to a clean, heatproof, nonreactive bowl. Stir in the butter, 1 tablespoon at a time. Cool to room temperature.
Yield: 2 1/2 cups