Add the sugar to a heavy nonreactive saucepan. Zest the lemons directly into the pot and set the lemons aside. Squish around the sugar and lemon zest until the sugar starts to feel a little moist from the oils.
1 1/2 cups sugar, 2 lemons
Add your lemon juice, salt, and gelatin to the sugar mixture and bring the heat to medium high, stirring periodically to dissolve your sugar. Don't let it boil.
While the sugar is heating and dissolving, separate six eggs to get your egg yolks, saving the egg whites for your cake. Whisk together the egg yolks and the remaining four eggs in a larger bowl than you think you'll need.
4 eggs, 6 egg yolks
As soon as the sugar is dissolved, remove the pot from the stove. While whisking the eggs, slowly pour the hot liquid into the eggs to temper them. If you don't whisk or if you pour too quickly, you'll end up with scrambled eggs. Once the mixture is fully incorporated, pour back into your saucepan and return it to the stove.
Cook at medium low heat for 10 or so minutes, stirring constantly with a whisk to keep anything from burning on the bottom. If you have a candy thermometer, keep cooking until it reaches 170 degrees.
Turn the heat off, and add the frozen butter. Once you add the butter, keep stirring constantly so that the fat is absorbed into your lemon curd.
1/2 cup unsalted butter
Use a fine mesh strainer and carefully pour your lemon curd into the strainer over a heat safe storage container.
Place plastic wrap atop it so that your lemon curd doesn't develop skin. Store it in the refrigerator until you're ready to use it. This will easily keep two to three days and still make a beautiful filling for a cake. Simply stir it up and use when you're ready!
This recipe makes enough to fill a 4 layer cake or one pie. I made my recipe dairy free by utilizing coconut oil in place of the butter. It worked beautifully and didn't change the flavor. If you have allergies, this is a great substitute.
You can make this without a candy thermometer, as well. If you don't have a thermometer, you'll know it's done when it starts to get really thick and darkens in color. When you can draw a line in your lemon curd with a spatula and the line remains after you've drawn it, you know it's done.
For more tips and tricks, be sure to read the full article above.