Prep. Prepare a mini muffin pan with liners, or grab a peanut butter cup silicone mold (note 4).
Chocolate layer. In a medium heat-safe bowl, melt chocolate (9 ounces) and coconut oil (2 tablespoons) together -- I do this by microwaving on high for 30 seconds and stirring the ingredients together with a rubber spatula before microwaving again. Don't over microwave, this will cause the chocolate to seize! Evenly divide half the chocolate into your prepared liners or mold. Place in the freezer for 10 minutes.
Peanut butter layer. Meanwhile, melt the coconut oil (2 tablespoons) and peanut butter (1/2 cup) together in a second medium, heat-safe bowl. Use a rubber spatula to stir in erythritol (1/4 cup) and salt (1/4 teaspoon) until they dissolve. Remove the muffin pan from the freezer, and spoon a dollop of peanut butter over the chocolate. Place pan back into the freezer for another 10 minutes.
Final layer. Remove from the freezer, and spoon the rest of the chocolate into the molds over the peanut butter layer. Option to sprinkle sea salt over peanut butter cups. Place in the freezer for 15-30 minutes, or until the peanut butter cups come out of their molds easily. Enjoy!
Peanut butter - Use nut butter of choice (almond is also delicious!), just read the ingredient list to ensure no sugar has been added. I always use no salt as well so I can adjust the salt level to taste.
Sweetener - Add more/less depending on your taste. Swerve and Lakanto are sweeter than other brands of erythritol, so keep that in mind if you're making a swap.
Chocolate chips - Lily's chocolate chips are my favorite for these peanut butter cups -- I always use milk, but they also make dark or semi-sweet.
Peanut butter cup silicone mold - Here's a great one on Amazon.
Nutritional information is based on 2 peanut butter cups, if you make 18 using this recipe.