**Option for cooking the curd in a 'bain marie', use a heat proof bowl placed over a pot of very shallow boiling water. Don't let the water touch the bowl, and cook as normal. May take a few extra minutes.
Zest 2 large lemons on top of the sugar and massage the zest into the sugar with your fingertips. Don't skip this step, as it helps the sugar absorb the oil in the zest to for extra citrus flavor.
2 tablespoons lemon zest
Stir in the 2 whole eggs and 2 egg yolks, whisking until the mixture is foamy and lighter in color. Pour in the lemon juice and add toss in the salt, whisk again.
2 large eggs, 2 large egg yolks, 125 grams/ml fresh lemon juice, 1/4 teaspoon fine sea salt
Cook on medium heat, continuing to slowly whisk until the mixture thickens. It should be thick enough to coat the back of a spoon and holds its shape when you draw a line through it with your fingertip. I always check mine with an instant thermometer to read 170℉ (72℃). About 5-7 minutes.
Immediately remove the pan from heat. Pour the curd through a fine wire mesh sieve into a separate bowl to catch any cooked egg or zest pieces.
While the curd is hot, stir in the softened butter. Whisk until the butter is fully melted, and the curd is smooth and glossy.
113 grams unsalted butter (European 82% butterfat is preferred)
Transfer curd to a heat proof glass container with a lid and store in the fridge. Or place in a bowl, covering with placing plastic wrap directly onto the curd to prevent a skin from forming.
Chill the curd for a minimum of 2 hrs to thicken before using.
Notes
Butter: Make sure butter is softened to room temperature so that it melts easily into the warm curd. Use European style butter with 82% butterfat for best flavor.Even Thicker Curd: For even thicker lemon curd use 6 large egg yolks and 1 teaspoon cornstarch.