To make salted caramel: pour sugar into a pan and heat over medium heat. Stir every 30 seconds until the sugar has melted completely. If sugar becomes clumped together, this is normal, continue to stir so that sugar does not burn.
Once the sugar has melted, remove from heat and add butter, stirring continuously. The mixture will bubble up quite a bit. Pour in heavy cream and add salt and continue to stir. (If the mixture begins to harden, add to low heat to liquify).
Pour into a heat-safe container and allow to cool.
Make the peanut butter filling by mixing together the creamy peanut butter, powdered sugar, and vanilla extract in a small bowl. If peanut butter is difficult to mix, simply microwave for 10-20 seconds.
Melt chocolate according to package instructions.
Line a muffin pan with muffin liners or silicone muffin/cupcake liners (preferred). Add 1 tbsp of chocolate to coat the bottom of the liners. Add to the refrigerator for 15 minutes.
Spoon in 2-3 teaspoons of peanut butter and 1 tsp of salted caramel. Cover with remaining melted chocolate. Return to the refrigerator for 20 minutes.
Remove peanut butter cups from the muffin liners and drizzle with additional salted caramel.