In a medium mixing bowl, cream together your butter and natural sweetener using a electrick mixer until light and fluffy.
Add your eggs, one at a time while mixing on low speed, then add your yolks. Continue to beat on low until the mixture is smooth and creamy.
Add the lemon juice and continue to mix on low speed until well incorporated. At this point your mixture will look lumpy and broken, but keep going.
Transfer your mixture to a medium sauce pan and place over low heat. Whisk until the mixture is headed and no longer lumpy.
Increase the heat to medium and stir constantly. Use a rubber spatula to scrape the bottom and sides of the sauce pan, until the mixture is thickened to a pudding texture.
Remove from heat, and sprinkle in your xanthan Gum on top and whisk it into your lemon mixture.
Transfer the mixture to a dish and place in the refrigerator to cool before assembling the dessert.