Beat butter and sugar in a large bowl using an electric mixer. Slowly add the eggs and the extra yolks one at a time.( Save the 2 egg whites for another recipe). Mix well after each addition. Pour in lime juice and mix again. Expect the mixture to look curdled, this is normal.
Cook the mixture over medium heat in a medium-size saucepan until it looks smooth (no longer curdled.) Increase the heat slightly and cook, whisking constantly, until the mixture thicken. Cooking thermometer should read 170^.
Remove the curd from the heat. Transfer to a bowl and press plastic wrap on the surface of the curd to keep a skin from forming.
Chill in the refrigerator.
The curd will thicken as it cools.
Covered tightly, it will keep in the fridge for a week and the freezer for 2 months.