Preheat the oven to 350°F (177°C). Line and grease three 6 inch cake pans. If you only have two pans, you can make this cake in batches. Sift the flour, cocoa powder, baking soda and salt in a large mixing bowl. Add in the sugars and mix them together.
Using a whisk attachment, start mixing on low and add in the eggs. After the eggs are mixed in, slowly add the buttermilk and vanilla extract while mixing on low.
Then add melted butter and coffee. After they are incorporated, start mixing on high for one minute, until the batter is light in color. Scrape the bottom with a spatula to make sure everything is properly mixed in.
Divide the batter between three cake pans and bake in the preheated oven for 25 to 30 minutes, until a toothpick inserted in the middle of cake comes out clean. Make sure not to overbake this cake or it'll lose it's moisture.
Take out the cakes from the oven, let them rest in the pans for 10 minutes, then gently take them out of the pans and let them cool down on a wire rack completely. You can also make the cakes a few days ahead. Just wrap them in two layers of plastic wrap and freeze them until ready to use.