Line a muffin tin with silicone liners or paper liners.
In a mixing bowl, beat together the peanut butter, powdered sugar, vanilla extract, and salt together until well combined.
Melt the chocolate in the microwave for 30 second intervals until melted or melt chocolate using the slow cooker method (preferred method--see below). Add in melted coconut oil, if using, to melted chocolate and stir until well distributed.
Using a small cookie scoop, place ½ tablespoon melted chocolate in each liner. Swirl the chocolate to cover the bottom of the muffin liner.
Place muffin tin in fridge or freezer for 5 minutes for chocolate to harden.
Once the bottom layer of the peanut butter cup has hardened, remove from fridge/freezer. Take about ½ tablespoon to 1 tablespoon peanut butter and form a disc that is just smaller than the mold so that there is room for chocolate to go around the edges. Place the peanut butter in the center of the chocolate base.
Place 1-2 teaspoons of the remaining melted chocolate over the peanut butter layer. Use a spoon to spread evenly.
Place the peanut butter cups back in the fridge/freezer for 5-10 minutes to harden.
Remove from silcone liners and serve or store in the refrigerator for up to 4 days (if they last that long.)
Melting Chocolate in Slow Cooker
Place chocolate in heat safe glass jar. Place jar in slow cooker and then carefully pour water into slow cooker until the water line reaches halfway up the jars. Be cautious not to get any water into the jar of chocolate.
Turn slow cooker on high, do NOT put lid on the slow cooker, and in about 30 minutes your chocolate will be perfectly melted (no need to stir while chocolate melts). Check on chocolate after 20 minutes, as all slow cookers vary in temperature.
Feel free to use almond butter or sunflower see butter in place of the peanut butter.
Feel free to use any chocolate you like. You can use chocolate chips, chocolate bars, or even leftover chocolate Easter Bunnies, chocolate Santas, etc. You can even use dairy free chocolate chips to keep these vegan peanut butter cups. Regardless of the option you use, be sure to chop your chocolate into small chunks, if not using chocolate chips, so that your chocolate will melt quickly and evenly.
The coconut oil is completely optional. I add it to help the chocolate harden faster and the form a thicker layer, but it is completely unnecessary.