Preheat oven to 350°F / 180°C degrees and line muffin tin with paper or foil liners.

Place chopped chocolate and cocoa in a large mixing bowl and pour hot coffee over mixture. Let it sit for 5 minutes, then whisk until smooth and chocolate has completely melted. Set bowl aside to cool.

Whisk flour, sugar, salt and baking soda together in medium bowl.

Whisk oil, eggs, vinegar and vanilla into cooled chocolate mixture until smooth, then add flour mixture to chocolate mixture and whisk until smooth.

Using a 2 ounce scoop (1/4 cup), divide batter evenly among cupcake liners, filling 2/3 full.

Bake until just set, 16 - 18 minutes.

Let cupcakes cool in tin for 10 minutes before transferring to wire rack to cool completely before frosting.

Combine egg whites and sugar in a bowl that will fit snugly on top of a pot of gently simmering water. The water should not touch the bottom of the bowl.

Whisk egg whites and sugar together until the sugar is completely dissolved. (I check this by rubbing the mixture between my thumb and finger - if it's smooth, it's done. If I still feel grains of sugar, it needs to cook longer)

Let the sugar mixture cool slightly, then transfer it to the bowl of a stand mixer fitted with whisk attachment, and whisk until you have room temperature stiff, glossy peaks.

Slowly add in small pieces of softened butter, making sure each piece is fully incorporated before adding in more. Add peppermint extract and continue whipping until buttercream is light and fluffy. Transfer to a piping bag, or a zip-top bag to frost cupcakes.