Preheat oven to 300°F. Grease and flour and spray 3 – 8 inch round cake pans. I use shortening to grease then dust the pans with flour. THEN I'll spray the pans with a cooking spray that contains flour. (VERY important you use a cooking spray that contains flour). This is a bit over the top when greasing pans, but this is what I do and I never having a cake that sticks.
In a medium bowl whisk the flour, sugar, cocoa, baking soda, baking powder, and salt.
In the bowl of a stand mixer fitted with paddle attachment mix the eggs, buttermilk, and veg oil until combined.
Add the dry ingredients to the stand mixer and mix until combined. Pour in the vanilla and hot water, mix on medium speed until combined.
Divide batter evenly between the cake pans and bake for 30-33 minutes or until a toothpick comes out with a few moist crumbs but no wet batter.
Remove cakes from the oven and and allow to cool for 10 minutes. Remove from the cake pans and allow cakes to cool on a cooling rack until just warm. (See note #1).
To frost the cake, place a cake layer on a cake stand, spread a little less than a 1/4 of the frosting on top of the cake in an even layer. Place the second cake round on top of the frosted cake round, continue by spreading an additional 1/4 of the frosting over the cake. Place the last cake round on top of the frosting. Use the remaining frosting to cover the top and sides of the cakes.