Preheat the oven to 350°F. Line two 12-cupcake pans with cupcake liners. Set aside.

Add the butter, sugar, salt, baking soda and vanilla to the bowl of a stand mixer fitted with a paddle attachment (or a large mixing bowl with a hand mixer.) Beat the ingredients for 5 minutes, or until the mixture is fluffy and has lightened in colour. Add the eggs one at a time, beating well after each addition.

In a separate bowl, sift together the flour and cocoa powder until it is lump free. Add about 1/3 of the flour mixture to the bowl and gently mix it in, scraping down the sides of the bowl from time to time. Add about 1/2 of the cooled coffee and then gently blend that in. Again, scrape down the sides of the bowl, then gently mix in another 1/3 of the flour mixture. Repeat with the scraping down, remaining coffee, then remaining flour, blending gently but well after each addition.

Divide the batter between the lined cupcake wells, filling each about 2/3 full. Tap the pan gently on the counter two or three times to remove air bubbles. Bake immediately for 23 to 25 minutes or until a toothpick inserted in the center of a cupcake comes out clean. Let the cupcakes rest in the pans for 5 minutes before carefully turning out onto a cooling rack. Let them cool completely while working on the icing.

In the bowl of a stand mixer fitted with a paddle or whisk attachment, or in a large mixing bowl with a hand mixer, whip together the butter and shortening until smooth and fluffy. Scrape the butter mixture into a clean bowl and thoroughly clean the mixer, bowl and the attachments.

Place the egg whites in the bowl of your stand mixer fitted with the whisk attachment (or in a large mixing bowl with a hand mixer.)

Add the corn syrup, sugar, and water to a medium saucepan over medium high heat. Stir until the sugar has dissolved completely. Add a lid to the pan, bring to a boil and boil the mixture for 3 minutes BUT DO NOT STIR!!. Remove the lid, add a candy thermometer to the pan and cook the mixture to the Soft Ball Stage (or 240°F).

While the syrup is cooking to the Soft Ball Stage, start mixing the egg whites on low speed. After a minute or so, they will begin to look foamy. When they reach that stage, add the cream of tartar and the salt, then raise the speed of the mixer to HIGH, beating to soft peaks. (In other words, when you raise the mixer, the whisk head should leave a little mound of egg whites that has a peak that curls back down on itself. Leave the mixer off.

When the syrup reaches the Soft Ball Stage, remove it from the heat immediately! Carefully pour about 1/4 of the hot syrup down the inside of the mixing bowl, taking care not to get the syrup on your skin! Turn the mixer on low and gradually increase the speed to beat the mixture well. Turn the mixer off again (See notes), and quickly add half of the remaining syrup. Turn the mixer on again and beat well. Turn the mixer off and add the final remaining syrup. Turn the mixture on high and beat well until the meringue has cooled to room temperature. Do not try to hurry this process or you'll have droopy icing at the end of all your work! Expect the process to take about 20 minutes.

When the meringue is completely room temperature through and through, pull off pieces of the butter and toss them into the mixer, beating well. If it starts looking like it wants to separate, stop adding butter and just beat until everything re-incorporates and looks airy. Finish adding the butter, then add in the melted chocolate and vanilla and whip until completely even in colour. If it is too soft to pipe or spread onto the cupcakes, you can refrigerate the mixture until it has a little more body. Pipe or spread the buttercream onto the cooled cupcakes and grate a dark chocolate bar over the top.