Preheat your oven to 350 degrees and prepare your cupcake pan with liners.
Sift your flour, cocoa, baking soda and baking powder into a large bowl. Add your sugar and salt - whisk until combined. Set aside.
Measure out your buttermilk, coffee, melted butter, eggs and vanilla and add to dry ingredients. Whisk for 1-2 minutes until there are no lumps.
Fill your cupcake liners 2/3 high with batter and bake for 10 - 12 minutes until they bounce back when touched OR when a toothpick comes out clean. Let them cool, or if you're impatient like I am, put them in the freezer for a few minutes.
Peanut Butter Swiss Buttercream
Add your egg white and sugar to a very clean bowl over a double boiler. Whisk them until the sugar is completely dissolved and the mixture is quite hot.
Using a stand mixer, clean the bowl with a few drops of lemon and wipe dry with a clean, new cloth. Whip the hot sugar and whites into a fluffy meringue for as long as it takes until the meringue is room temperature, not hot.
While still whisking, slowly add your room temperature butter one cube at a time until it's thoroughly incorporated. Add your vanilla and salt. Follow with your peanut butter, tasting inbetween additions. You can really add as much or as little as you like.
Pipe or use an offset to decorate your cupcakes. Make sure the cupcakes are completely cooled or the icing will slide off - disastrous!