Whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat the butter and sugar with an electric mixer until light and fluffy. Add the eggs one at a time, beating well after each addition.

Gradually add the dry ingredients to the butter mixture in three portions, alternating with 2 portions of buttermilk. Mix until just combined.

Stir in the vanilla extract and hot water. The batter will be thin.

Divide the batter evenly between the two prepared cake pans. Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.

In a small saucepan, whisk together the milk and flour over medium heat. Cook, stirring constantly, until the mixture thickens into a smooth, pudding-like consistency (about 5-7 minutes).

Remove from the heat and whisk in the sugar and salt. Let it cool completely to room temperature. Then cover it with plastic wrap, pressing the wrap directly onto the surface to prevent a skin from forming.

In a large mixing bowl, use an electric mixer to beat the butter until light and fluffy (about 3-5 minutes).

Gradually add the cooled milk-flour mixture to the creamed butter, one spoonful at a time, beating until smooth and fluffy. The frosting should become light and airy.

Mix in the vanilla extract, beating until well combined. (It should have a light, fluffy, and silky consistency. It’s a bit like whipped cream but with more structure.)

Place one cake layer on a serving plate. Spread a layer of frosting on top. Place the second cake layer over the first and frost the top and sides of the cake.