Grease the base of two 8-inch round cake pans; line with parchment paper. Combine butter, sugar, flour, cocoa, baking powder, baking soda, salt and eggs in a large bowl. Using an electric mixer set on medium, beat until smooth. Continue beating until increased in volume, about 2 minutes longer. Add the hot water and beat to incorporate, about 1 minute longer. Divide batter between pans.