Preheat oven to 180°C/350°F/Gas 4. Line a cupcake pan with 24 liners and set it aside.
Using an electric handheld or standing mixer, beat the cake mix, butter, milk, and eggs until combined.
Fill the cupcake liners about three-quarters full.
Place into the oven and bake for 20 minutes or until an inserted toothpick comes out clean.
Remove from the oven and leave to cool for 5 minutes in the pan, before transferring to a wire rack to cool completely before decorating.
To make the frosting, use an electric handheld or standing mixer and beat together the butter, peanut butter, powdered sugar, heavy whipping cream, and vanilla extract until combined, smooth, and holds a peak.
Scoop 1 cup of the frosting into a piping bag fitted with a star tip and set it aside.
Pour the sprinkles into a bowl.
Using a medium ice cream scoop, divide the frosting onto the cupcakes and smooth lightly into a thick disk using a butter knife or palette knife.
Dip the frosted cupcakes into the sprinkles to cover completely.
Pipe a swirl of the reserved frosting on top of each cupcake.
Place a halved Reese's Peanut Butter Cup on top of each cupcake.
Enjoy and Happy Fall Y'all!