Cube butter and place back in the fridge to keep it cold.

Zest 1 whole lemon.

Juice lemon and remove any seeds.

Combine lemon and sugar in a food processor and pulse to combine well.

If you haven’t already separated the whites from the yolks, you can do that now and set whites aside for another recipe, they freeze well.

Create a double boiler by placing a glass bowl over a pan with a few inches of water in it.

Whisk lemon juice and sugar together in the bowl of the double boiler.

Add in eggs and whisk to combine well.

Cook over medium heat, whisking constantly until the mixture thickens, about 8 to 9 minutes. To test readiness, stir with a metal spoon, flip it over, and run your finger over the back, the thickened mixture should not run.

Remove from heat and immediately whisk in your butter until it is completely melted and combined( you can also do this just before removing it from the heat.

You can pour it directly into your jars or run it through a sieve first to make it extra smooth and creamy.

Wipe off the rims and replace the lids and rings.