6tablespoons(85 grams) unsalted butter room temperature (65-68°F)
Place a strainer over a large bowl, near the stove. Use a 2 or 3-quart non-reactive saucepan for this dessert.
Place the eggs yolks, whole eggs and sugar in the saucepan and whisk until it is well blended. Stir in the lime juice, and salt.
Cook the mixture over medium heat, whisking constantly until the mixture is thickened and is 185 degrees F. It should coat the back of wooden spoon and leave a visible trail when you run your finger through it. When the mixture has thickened and reached temperature remove the saucepan from heat and whisk in the butter 1 tablespoon at a time.
Pour the lime curd into the strainer and press it through the strainer with a spatula. Zest the lime directly into the curd and gently stir the zest into the warm curd.
Cover the surface of the curd with plastic wrap, gently pressing the plastic wrap onto the surface of the curd. Place the curd in the refrigerator and chill for at least 2 hours.
The curd is good in the refrigerator for up to 2 weeks. It can be frozen for up to one year. When ready to use, thaw it in the refrigerator for 24 hours before ready to use.
A nonreactive saucepan is either tainless steel or enamel-coated cast-iron. A reactive pan, such as aluminum, will react with acid in the lime curd and affect the taste of the curd.