These cookies are beloved by kids of all ages. Chocolatey, chewy, and peanut-buttery, they'll disappear fast! Unwrap the mini Reese's cups ahead of time and have them ready to immediately press into the cookies after they are taken out of the oven.
Preheat the oven to 350°F. Coat the cavities of a mini muffin pan with flour-based baking spray (or grease pan with nonstick cooking spray).
In small bowl, whisk together the flour, cocoa powder, baking soda and salt.
In the bowl of an electric mixer, beat the sugar, peanut butter, and unsalted butter on medium speed until well combined, about 2 minutes. Beat in egg, whipping cream, and vanilla. Beat in the flour mixture on low speed until blended.
Shape dough into 3/4-inch balls. (I used a cookie scoop, 4 teaspoon capacity.) Place one ball into each muffin cup.
Bake 12 minutes. Immediately press 1 peanut butter cup into center of each cookie. Cool in pan on cooling rack.
Combine the peanut butter chips and oil in a small microwave-safe bowl. Heat in 30 second intervals until the mixture can be stirred smooth. It should be a little runny and pourable. Transfer the mixture to a zip-top bag with a tiny hole in the corner snipped. Drizzle over hot cocoa bombs. Let stand until set, about 15 minutes.
Drizzle the peanut butter mixture over 5 cookies at a time, then immediately top with sprinkles. Continue working like this until all of the cookies are drizzled and sprinkled. The peanut butter drizzle will set up quickly, so be swift with your sprinkling.
Allow the cookies to stand until set, about 5-7 minutes. Store the cookies airtight until ready to serve.
Notes
Place the unwrapped peanut butter cups on a plate and then on a countertop away from the stovetop. This prevents them from softening and melting. They should be firm enough to press into the hot cookie cups right when they come out of the oven. If your kitchen is particularly warm at room temperature, place the peanut butter cups in the refrigerator while the cookies bake.