Combine the zest of 2 lemons and the white sugar together with your fingers until it's well combined and the sugar is fragrant. Set aside.
Cream the butter with a hand mixer until creamy and smooth. Add the fragrant sugar and blend until well combined. Add the eggs, one at a time, and mix thoroughly. Add the lemon juice and salt and blend until well combined.
Pour into a small saucepan and cook over medium heat, stirring often, until thickened, about 10 minutes at about 170 degrees. Remove from heat and let cool before pouring it into a container. Serve over crepes, pancakes & waffles, toast, or muffins. Store, well-sealed, in the refrigerator. Enjoy.