Preheat oven to 350ºF. Butter two 8-inch round pans and dust with cocoa.
Combine cocoa, flour, sugar, baking soda, baking powder and salt into the bowl of a mixer. Beat on low until combined.
Add eggs, buttermilk, water, oil and vanilla. Increase speed to medium and beat until very smooth, about 3 minutes.
Divide batter into pans. Bake until set about 30-35 minutes. Let cool completely before turning out and frosting. Dust with Maldon or Kosher salt.