Line a 9" x 5" loaf pan or an 8" x 8" cake pan with parchment paper, leaving a few inches of overhang on two sides to lift the fudge out later.

In a small saucepan, combine the following: 116-ounce jar unsweetened creamy peanut butter, 2/3 cup sugar-free confectioners sweetener, 1/3 cup ghee or coconut butter, 3 Tbsp Marine Collagen or beef collagen (optional), 1/8 tsp sea salt, 1 tsp pure vanilla extract (optional), and 1/2 tsp ground cinnamon (optional).

Heat the saucepan over medium-low. Stir constantly until the mixture is fully melted and smooth, and all ingredients are well combined. Do not boil; remove from heat as soon as the mixture is evenly creamy.

Pour the warm peanut butter mixture into the prepared pan and use a spatula to smooth it into an even layer.

Place the pan in the freezer and chill for at least 2 hours, or until the fudge is firm and set.

Remove the pan from the freezer, use the parchment overhang to lift the fudge out, and transfer it to a cutting board. If desired, let it sit at room temperature for a minute to ease cutting, then cut into squares with a sharp knife.

Store leftovers in a zip-top bag in the freezer.