Preheat oven to 350º with rack in the center. Spray two 9x2 inch round cake pans with non-stick spray.
Whisk together flour, sugar, cocoa, baking soda, and salt in a large mixing bowl. (Don't use a mixer.)
Combine water, oil, vinegar, instant coffee, and vanilla in a large measuring cup. Add to the dry ingredients and whisk just until combined, a few lumps are OK.
Divide batter between pans, then bake until a toothpick inserted in the center comes out clean, 35-40 minutes.
Cool cakes on a rack for 15 minutes, then invert them onto the rack.. Leave cakes upside down (this flattens domed cakes) to cool completely.
*I made the following high altitude adjustments: Decreased the sugar by 2 tablespoons, used 1 ½ teaspoons baking soda and 2 ¼ cup hot water.