Preparation

• Add 1-2" of water to the bottom of a medium saucepan. Bring water to a boil, then reduce heat to low and keep water simmering.
• Place a glass (and heat-proof) bowl on top of the saucepan, so the bottom isn't touching the water.
• To the glass bowl, add sugar, lemon juice, egg yolks, and lemon zest. Whisk to combine well.
• Continue cooking, and whisking nearly constantly for about 8-10 minutes. Curd should be thickening.
• If your lemon curd isn't thickening at all, increase the heat to medium low and continue whisking and cooking.
• Remove pan from heat, then add butter and whisk to melt completely.
• Transfer lemon curd to a large bowl, or smaller containers. Place a piece of plastic wrap directly on top of the curd, pressing very gently so the entire top surface is covered. This prevents a 'skin' from forming on the curd.
• Let curd come to room temperature, then place in the refrigerator for at least 1-2 hours. Once cooled, the plastic wrap can be removed.
• Curd will thicken more as it cools and chills.
• Lemon curd will keep in the refrigerator for 1-2 weeks, or can be frozen for up to 3 months.