Preheat the oven to 350°F.

Line a standard cupcake pan with cupcake liners.

Add the chocolate fudge cake mix, eggs, whole milk, and softened butter to a large mixing bowl.

Using a hand mixer, beat the ingredients together until they're completely combined and the batter is smooth.

Be sure to scrape down the sides and bottom of the bowl so there are no pockets of dry cake mix remaining.

Divide the chocolate cake batter between your prepared cupcake liners, filling each approximately ¾ full.

An ice cream or cookie scoop can make this much easier and help ensure all of your cupcakes are roughly the same size.

Bake the cupcakes for approximately 18–21 minutes, or until a toothpick inserted into the center of a cupcake comes out clean or with just a few moist crumbs.

Remove the cupcakes from the oven and allow them to cool in the pan briefly before transferring them to a cooling rack.

Let the cupcakes cool completely before decorating.

If they're still warm, that gorgeous peanut butter frosting will start to melt.

While your cupcakes are cooling, you can prepare the frosting.

Add the softened butter and creamy peanut butter to the bowl of a stand mixer.

Beat until smooth and creamy.

Gradually add the powdered sugar, followed by the vanilla extract and heavy whipping cream.

Continue beating until the peanut butter frosting is light, smooth, and fluffy.

If the frosting seems too thick, add a tiny amount of additional heavy cream. If it's too soft, add a little more powdered sugar.

Prepare the Cupcakes for Decorating

Scoop approximately 1 cup of peanut butter frosting into a piping bag fitted with a large star tip. Set it aside for the final decoration.

Pour your fall sprinkles into a shallow bowl.

Now you're ready for the fun part!

Using a medium ice cream scoop, place a generous scoop of peanut butter frosting on top of each cooled chocolate cupcake.

Gently smooth and shape the frosting into a thick, rounded disk or mound.

Carefully press or roll the frosted portion of the cupcake into the bowl of fall sprinkles until the frosting is generously coated.

Using the reserved piping bag, pipe a small decorative dollop of peanut butter frosting onto the center of each cupcake.

Finish by pressing half of a Reese's Peanut Butter Cup into the frosting.

Your harvest cupcakes are ready to serve!