In a microwave, melt the butter and peanut butter together for a minute. Stir, and then microwave in 30 second increments until the peanut butter is soft and can be easily blended.
Add the caramel flavoring, and using a hand mixer, blend the mixture until smooth.
Add the Swerve, 3 to 4 ounces at a time, blending thoroughly after each addition. Scrape down the sides if necessary. Blend until all the Swerve is evenly incorporated.
Spread the warm fudge into an 8x8 baking pan that's been lined with parchment paper, sprinkle with salt to taste, and refrigerate for at least 2 hours before cutting into 20 evenly-sized pieces.
Macros for 1 piece: 124 calories, 1 gram net carbs, 2 grams protein, 11 grams fat.