Preheat the oven to 350ºF or 180ºC and line a 12 hole cupcake pan with cupcakes liners.
Sift the cocoa powder into a large mixing bowl and pour over the boiling water. Mix into a smooth paste.
Add all remaining cupcake ingredients and mix with an electric hand mixer or stand mixer until combined, scraping the sides of the bowl as you need.
Scoop the cupcake batter into the liners evenly. Bake for 18-22 minutes or until the top of the cupcake bounces back when you touch it.
Leave the cupcakes in the pan for about 10 minutes to cool, then transfer them to a wire rack to cool completely.
Make the frosting:
Add the peanut butter, room temperature butter (not melted) and vanilla extract to a large mixing bowl. Mix with an electric hand mixer or stand mixer until smooth and creamy.
Gradually sift in the powdered sugar a little at a time, mixing after each addition. When the mixture starts to become a little too thick, add the cream 1 tablespoon at a time until a pipeable consistency is reached.
Mix the frosting for another minute or so to get it super smooth.
Frost and decorate the cupcakes:
Spoon, spread or pipe swirls of the peanut butter frosting on top of each cupcake. I used a Wilton 1M piping nozzle.
If adding the dark chocolate drizzle, heat the chocolate chips in the microwave in 20-30 second bursts, stirring between each interval, until melted. Using a small spoon, drizzle chocolate over the top of each frosted cupcake.
Add mini peanut butter cups on top (optional).
Store in an airtight container at room temperature.
The calories shown are based on the recipe making 12 cupcakes, with 1 serving being 1 frosted cupcake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**