In a medium mixing bowl, whisk together the melted coconut oil, unsweetened cocoa powder, powdered erythritol, vanilla extract, and salt until smooth.
Line a muffin tin with 6 muffin cups. Spoon 1-2 tablespoons of the chocolate mixture into each muffin cup, making sure to evenly distribute it.
Freeze the muffin tin for 10-15 minutes or until the chocolate has hardened.
Spoon 1 tablespoon of peanut butter on top of each chocolate cup.
Pour the remaining chocolate mixture on top of the peanut butter to cover it.
Freeze the muffin tin for another 20-30 minutes or until the chocolate has hardened.
Remove the peanut butter cups from the muffin tin and enjoy!