Whip the butter and cream cheese together until fluffy.
Mix in the sweetener and vanilla extract. Stir until well combined.
Divide the mixture into 12 silicone muffin liners or spread into an 8x8-inch baking dish lined with parchment paper.
Wrap the liners or dish tightly in plastic wrap, then place in the freezer for at least 3 hours. Overnight is fine. When you're ready to enjoy them, let your fat bombs sit at room temp for 10 minutes or so for the best texture.