Preheat oven to 350 degrees F. Line a cupcake pan with liners.
In a large bowl, sift together the cocoa powder, flour, salt and baking soda. Whisk together to combine together.
Pour in the buttermilk, vegetable oil, egg, sugar, and vanilla to the flour mixture and mix together until well combined.
Slowly pour in the hot coffee and mix again until combined. NOTE: The batter will be on the thinner side. Don’t worry as it will bake up just fine.
Fill a cupcake liners about 3/4 of the way full with batter and lightly add the peanut butter cup to the top. Don’t push down the peanut butter cup as it will sink during baking.
Bake for 19-22 minutes, until a toothpick comes out clean. Completely cool before frosting.
Frost the cupcakes and if you like, garnish with a thin peanut butter cup.
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Notes
Homemade Buttermilk substitute: Make your own "buttermilk" at home by adding 2 teaspoons vinegar or lemon juice to 1/2 cup of milk. Let the milk sit for 5 to 10 minutes until curdled. Use as directed.Do not press the peanut butter cup into the batter. Just rest it on top of the cupcake batter before baking.Pressing down on the Reese's causes it to sink all the way to the bottom.Toss peanut butter cups in flour to help prevent sinking if desired.
Why is coffee added to the chocolate cupcakes?
This is an old baker's trick! Adding coffee to chocolate recipes gives the chocolate a richer flavor but there is no coffee taste.
What can I use instead of coffee?
Just substitute water or milk.
Storing the cupcakes
Refrigerator: Store them in an airtight container for up to 4 days.Freezing the CupcakesHow to freeze unfrosted cupcakes (recommended)For best results, freeze baked cupcakes before frosting. When ready to eat, thaw and pipe on the frosting before serving.
Allow them to cool completely.
Wrap individually in plastic wrap.
Place them in a freezer-safe airtight container.
How To freeze frosted cupcakes
Once cooled cupcakes are frosted, place them on a rimmed baking sheet in the freezer to fully freeze (1-2 hours). Allow space in between them.
After they are frozen, wrap each cupcake individually in plastic wrap.
Transfer all the wrapped cupcakes to an airtight container and keep frozen for up to 1 month.
To thaw frozen frosted cupcakes, remove the plastic wrap and allow them to sit at room temperature until thawed; about 1 hour.Make sure no cupcakes are touching one another (to preserve the frosting shape).