Preheat the oven to 350, and place an oven rack in the center position of the oven.

Spray one 6" cake pan with 2" sides with cooking spray, and then line the bottom with a circle of parchment paper and spray again.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda and salt.

In a large measuring cup, whisk together the oil, vanilla, vinegar, and coffee.

Slowly pour the coffee mixture into the bowl while whisking. Whisk until the cake batter is mostly lump-free, but try not to mix too much and make a dense cake batter.

Scrape the batter into the prepared cake pan, and bake on the center rack of the oven for 32-34 minutes, until a toothpick inserted into the cake comes out clean.

While the cake cools, make the frosting: beat together the softened 'butter' with the powdered sugar, cocoa powder, vanilla, pinch of salt and 1 tablespoon of coffee. Add the remaining coffee if needed to bring it together.

Once the cake is cool, slice it in half horizontally. Place the bottom of the cake on a plate, and scoop 1/3 of the frosting on top. Spread the frosting almost to the edges. Place the remaining cake layer on top, and frost with the remaining frosting.

If desired, portion some frosting into a bag fitted with an open star tip and decorate the cake with buttercream roses and sprinkles.