Preheat an oven to 350°F (180°C) and prep a cupcake pan with liners.
In a large mixing bowl, add the cocoa powder, sugar, oil, vanilla, and eggs. Mix with a whisk until combined and smooth.
Add the flour, baking soda, and mix until almost combined.
Add the hot coffee and mix until well combined. Do not overmix, just until there are no lumps of flour visible.
Use an ice cream scoop to fill out the cupcake ⅔ full (do not overfill) and bake in a 180°C (350°F) preheated oven for about 20 minutes or until a toothpick comes out clean with a few moist crumbs.
Cool the cupcakes for 10 minutes and transfer them to a cooling rack to cool completely (don’t frost warm cupcakes).
Make the peanut butter frosting
Into a large bowl, add room-temperature butter, peanut butter, vanilla extract, heavy cream, and salt, and mix with a hand mixer or stand mixer until the mixture is light and fluffy.
Then add ½ of the powdered sugar at a time (you don’t want to be in a powdered sugar cloud) and mix until smooth and silky.
If the frosting is too thick, add a splash more cream, one tablespoon at a time, until you reach your desired consistency. If it’s too thin, add a little extra powdered sugar.
Assembly
Make a small hole in the middle of each cupcake. I used a butter knife; you can also use a cupcake corer. Fill the hole with peanut butter until just full.
Transfer the peanut butter buttercream to a piping bag with a round tip and frost the cupcakes. Top them with a mini peanut butter cup and serve!
Notes
Use room temperature ingredients. Eggs, and buttermilk should all be at room temperature. This helps everything blend smoothly and gives your cupcakes a light, even texture.
Use cupcake liners to prevent the cupcakes from sticking to the pan, making them easier to remove and creating a more professional appearance.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Don't overmix the batter. Once you've added the dry ingredients, mix just until they're incorporated. Overmixing can lead to tough, dense cupcakes.
Use a round piping tip. For a bakery-style look, pipe tall swirls of frosting with a large round piping tip. It gives the cupcakes a professional finish.
Use a cookie scoop for even cupcakes. This ensures all cupcakes bake evenly and look uniform, no tiny or overflowing cupcakes here!
Don't overbake the cupcakes. Keep an eye on the cupcakes as they bake and remove them from the oven as soon as a toothpick inserted in the center comes out clean or with a few moist crumbs.
Allow the cupcakes to cool completely before frosting them with the frosting. This will prevent the frosting from melting and sliding off the cupcakes.