Preheat the oven to 180 C (350F). Grease and line a standard sized loaf pan (9x5 inches) with parchment paper.
Mix the cocoa powder and hot coffee together in a small bowl until cocoa powder is dissolved.
In another bowl, mix together the flour, baking powder, and salt and set aside.
In the bowl of a stand mixer fitted with a paddle attachment, combine the butter and sugar until light and creamy, 3 minutes.
Add the eggs one at a time, mixing for 1 minute after each addition. Mix in the vanilla. Add the flour mixture until combined, then add the chocolate coffee mix, then the buttermilk.
Fold in the chocolate chips with a spatula, and transfer the batter to the prepared loaf pan. Bake for 50-60 minutes or until the top is set and a toothpick inserted comes out clean. Cool for 20 minutes, then turn the pan over to remove cake from the pan.
Continue cooling cake completely, and meanwhile make the glaze. Sift together the icing sugar and the cocoa powder, Stir in the salt and vanilla, then add 2 tablespoons of milk or water. Continue adding liquid 1 tablespoon at a time or until desired consistency (don't exceed 4 tbsp).