Line an 8×8” pan with parchment paper and grease.
Add chocolates and Keto Chow to a mixing bowl. A stand mixer will work best but a hand mixer will also work. Set aside.
Butter the sides of a large, lidded, heavy pot with your stick of butter. Pour in the cream and xylitol and stir together. Place over medium heat and stir constantly until it comes to a rolling boil.
At this point, cover with a lid for one minute and then remove lid. Make sure to set a timer. Continue cooking on medium heat until the mixture reaches 230℉ on a candy thermometer. This should take about 2-3 minutes, but it is best to use a thermometer. Do not overcook or leave on the heat too long, or the fudge will crystallize and harden.
Remove from heat and add the remaining butter, the vanilla extract, and mint extract. Let them sit for one minute in the candy mixture without stirring. Pour the mixture over the chocolates and Keto Chow. Do not scrape the pot. Beat fudge on low for two minutes, then on high for five minutes. (Be sure to whip for that full time.) It will have the texture of a soft marshmallow cream.
Pour into the prepared pan. Cover and refrigerate until set—at least four hours, or overnight.
To cut, remove slab with parchment paper and use a sharp knife to cut into even squares. Keep refrigerated in a sealed container.