Line a 6-cup muffin tin with silicone liners or paper liners. Alternatively, line a 12-cup mini cupcake liners.

In a mixing bowl, beat together the peanut butter, powdered sugar, vanilla extract, and salt together until well combined. Set aside.

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.

Store the peanut butter cups in the refrigerator for 4-5 days in an airtight container.

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.