4 Egg Yolks
2/3 cup Sugar
1 Tablespoon Lemon Zest
1/3 cup Lemon juice, 2-3 lemons
6 Tablespoons Butter, softened and cut into 6 pieces
Fill the bottom pot of your double broiler with 1-2 inches of water. Place on high heat. Once the water begins to boil, reduce to low heat and keep water at a simmer.
Place egg yolks, sugar, lemon zest and juice in to the pot on top of your double broiler. Wisk until completely blended, then continue to whisk as the curd cooks. Constant whisking prevents the egg yolks from curdling. Whisk and cook until the mixture becomes thick, resembling the texture of hollandaise sauce, about 5-10 minutes. If it is not thickening, turn up the heat while constantly whisking.
Remove pan from heat. Whisk the sliced butter into the curd. The butter will melt from the heat of the curd as you whisk. Pour curd into a jar and place a piece of plastic wrap directly on top so that it is touching the top of the curd. The curd will continue to thicken as it cools. Once completely cool, remove the plastic wrap and refrigerate for up to 10 days.