Preheat oven to 350F. Liberally spray three 9-inch round pans with nonstick baking spray.
Add eggs and sugar to bowl of stand mixer fitted with paddle. Mix on high speed for about 3 minutes.
Combine cocoa powder, instant coffee, and hot water in small bowl and mix until smooth. Decrease speed to medium and add chocolate mixture to eggs and sugar.
Sift flour, baking soda, baking powder, and salt in small bowl. Decrease speed to low and add to stand mixer.
Add in buttermilk, vegetable oil, and vanilla and beat until just combined. Batter will be thin; this is normal.
Evenly add cake batter to prepared pans and bake until toothpick in the center comes out with a few moist crumbs attached, about 22-25 minutes.
Remove cakes from oven and cool in pans for 10 minutes. Then gently remove cakes from the pans and place on a wire rack and allow to cool fully, an additional 20 minutes.