In a small saucepan over medium-low heat melt the butter and sweetener. Cook until slightly thickened. Remove from the heat and cool for 5 minutes.
Whisk in the egg yolks one at a time. Return to the stove and cook over medium-low heat until thick.
Add the lemon juice and whisk until smooth. Add the cream and whisk again. Strain through a fine mesh strainer in case there are any bits of scrambled yolk.
Cool to room temperature. Refrigerate for 3-4 hours to set before serving.
