Preheat the oven to 350 F. Line 20 cupcake cavities with paper liners.
In a bowl, sift together the flour, cocoa powder, baking soda, and salt. In a separate bowl or large mixing cup, whisk together the buttermilk, sour cream, and water (or coffee).
In the bowl of a large stand mixer fitted with a paddle attachment, beat together the butter and sugars until they’re light and fluffy, about 3-5 minutes. Add the eggs one at a time, beating well after each addition, then add the vanilla extract.
With the mixer running on low speed, add a quarter of the dry ingredients. When it’s mostly mixed in, add a third of the liquid ingredients. Continue to alternate adding drys and liquids, ending with the dry ingredients. When the drys are almost all mixed in and only a few streaks of flour remain, stop the mixer and finish mixing by hand with a spatula. Scrape down the bottom and sides of the bowl.
Scoop the batter into the lined cupcake pans. Bake in the preheated oven for 22-25 minutes, until the tops of the cupcakes spring back when lightly pressed. Cool completely.
To Make the Filling:
Don’t make the filling until you’re ready to fill the cupcakes. Combine the caramels, cream, and butter in a microwave-safe bowl. Microwave in 30-second increments, stirring well after every 30 seconds. They may resist melting and coming together at first, but continue to stir and heat until you have a smooth, fluid mixture. Add the chopped peanuts and stir them in.
To Make the Frosting:
Combine the butter and peanut butter in the bowl of a large stand mixer fitted with a whisk attachment, and beat on medium-high speed until light and fluffy. Add the vanilla, cream, and powdered sugar, and mix on low speed until the sugar is moistened. Raise the speed to medium, and continue to beat until the mixture lightens and becomes fluffy and smooth. Add the marshmallow cream and stir it in by hand using a rubber spatula, scraping the bottom and sides of the bowl well. Once the frosting is well-mixed, spoon it into a pastry bag fitted with a large star tip.
Use a sharp paring knife to cut a cone-shaped hole out of the top of the cupcakes. Scoop the caramel-peanut filling into the hole, coming almost all the way to the top. Cut the bottom off of the cupcake cone, and replace the top of the cupcake on top of the caramel. (The cupcake filling can be eaten or thrown away—I trust you will find something to do with it.) If the caramel starts to get a little hard to work with, microwave it briefly until it is fluid again.
Once all of the cupcakes are filled, pipe the frosting on top in one big decorative swirl. Add a drizzle of fudge sauce or chocolate ganache, a sprinkling of chopped peanuts, and half of a fun-sized Snickers bar on top. Store Snickers Cupcakes in an airtight container at room temperature, and enjoy within 3-4 days.