Line a mini muffin tin with paper liners and set aside.
Line a cookie sheet with wax paper and set aside.
In a medium saucepan over medium heat, stir together the peanut butter, butter, and brown sugar. Once the mixture is completely melted and begins to bubble lightly, remove it from the heat.
Add the powdered sugar 1 tablespoon at a time, stirring until smooth.
Let sit until cool enough to handle, about 5 minutes.
Melt and temper 1 cup of the chocolate (or melt 1 cup of Wilton Candy Melts), and pour just enough into each muffin cup to cover its bottom.
Tap the tin gently against a hard surface to even out the chocolate.
Refrigerate for about 30 minutes.
Roll the peanut butter mixture into teaspoon-size balls, using your hands, and place on the prepared cookie sheet, spacing evenly. They may flatten immediately, depending on how warm your mixture is. If
they don’t, use your hands or a rubber spatula to flatten the balls into disks about ½ inch thick. Refrigerate for 20 minutes.
To assemble your peanut butter cups, place one peanut butter disk on top of each chocolate-coated liner, making sure to leave room on the sides and top of the cups.
Melt and temper the remaining 1¼ cups chocolate (or melt the remaining Wilton Candy Melts), and pour it on top of the peanut butter filling. Once again, tap the tin gently against a hard surface to even out the chocolate.
Refrigerate for 30 minutes, or until solid. Sprinkle with salt, if using.