Step 1

In a glass or ceramic bowl set over a pan of barely simmering water, whisk together the eggs, sweetener, lemon juice, and lemon zest. Whisk continuously until the mixture thickens, about 10 minutes. Watch carefully as it will thicken all of a sudden.

Step 2

Immediately remove from heat and add the butter. Let sit a few minutes to melt and then whisk until smooth and creamy.