Preheat the oven to 350°F. Lightly grease two 8-inch round cake pans, dust lightly with flour and line the base with rounds of parchment paper.

Make the cake. Use a fine mesh sieve to sift flour, cocoa powder, baking powder and baking soda into a large bowl. Add sugar and salt and whisk to blend very well so the ingredients are evenly combined.

Prepare the water and keep it hot. Set it aside while you prepare the batter.

Combine eggs, oil, sour cream and vanilla in a medium bowl and whisk to blend well. Pour into the bowl with the dry ingredients and mix with an electric handheld mixer on medium-low until blended. You can also mix by hand with a wire whisk. It will be thick and somewhat dry. Add the hot water gradually in two stages to minimize clumps forming and mix until evenly combined and the batter is smooth. The batter will be quite thin.

Divide batter evenly between the prepared pans and tap the pans on the countertop to allow any large air bubbles to surface and pop. Bake for 30-33 minutes until cakes spring back when pressed gently and a skewer inserted into the center comes out clean. Transfer pans to a wire rack and let cool for 15 minutes before running a knife or offset spatula around the sides and inverting the cakes onto the rack to cool completely.

Make the frosting. Prepare the Milk Chocolate Frosting according to this recipe here.

Use a large offset spatula to spread the frosting over the cooled cake layers right away.