Melt ½ cup butter in a small saucepan on low heat.
½ cup butter
Remove from heat and whisk in ⅔ cup erythritol, ½ cup lime juice, and zest from 1 lime until dissolved.
⅔ cup erythritol, ½ cup lime juice, 1 lime
Whisk in 6 egg yolks and return to the stove over low heat.
6 egg yolks
Cook over same low heat, whisking continually until it starts to thicken.
Remove from the heat. Whisk in ¼ teaspoons xanthan gum and 1 tablespoons gelatin until dissolved and smooth.
¼ teaspoons xanthan gum, 1 tablespoons gelatin
Pour this filling over the crust and spread out evenly.
Bake the bars at 350 degrees F / 176 degrees C for 15 minutes.
Remove from oven and cool for 30 minutes.
Cut into 2 x 2-inch squares.