2In a double boiler, once the water is simmering lightly add mixture into top bowl or top boiler pot.
3Stir until the erythritol is fully melted, takes approx 5 minutes. Test yolk mixture with fingers to make sure there is no grittiness. Keep stirring until smooth. Do not boil or the eggs will begin to cook.
4Once smooth remove from double boiler, transfer into a large mixing bowl that is room temperature.
5Whip on high for approx 15 minutes. Until high foam thickness in a meringue form.
6Slowly add in one cube of room temperature butter at a time, waiting until it is completely mixed in before adding the next, the meringue will flatten and turn into more of a cream base now. Keep adding in the butter until It's all incorporated.
7Whip on high for 2-3 minutes to fluffen up the icing. While mixing add in vanilla. You may also add in other desired flavoring. I recommend staying away from oil based flavors. You can even add in a little bit of melted chocolate if you want a richer flavor.
8If while mixing in the butter your icing went a tad soupy, set in the fridge for 5-15 minutes and whip again. All is not lost.