Get all your ingredients ready.
Thoroughly whisk eggs in a bowl.
Add whisked eggs, sugar, lemon juice, and zest in a medium-size saucepan. Whisk ingredients thoroughly. Next, add the cubes of butter to the egg mixture. Note that the butter will melt in the next couple of minutes of cooking.
Turn on burner to the lowest heat setting
Place the saucepan on the stove and constantly stir with a rubber spatula. The heat should be at the lowest setting. Make sure not to boil curd, or it will split. Stir with a spatula for 25 minutes.
After 25 minutes, increase the heat to a low-medium flame. Stir constantly. The curd goes from a liquid yellow color to an opaque creamy color in the last two minutes of cooking. It will thicken quite nicely in the last 5 minutes.
Once it thickens, take off the stovetop and immediately transfer the cooked curd to a bowl. Make sure to keep stirring for a couple of minutes as it cools. If you get bits of scrambled egg, strain the curd or pluck out the bits of egg. The scrambled egg won't doesn't affect the flavor but just an aesthetic choice.
This recipe makes 2 cups of lemon curd. Pour into a clean jar and place in the fridge once cooled. The lemon curd should last for about 1-2 weeks in the refrigerator.