• Preheat the oven to 350°F. Grease two 9-inch round cake pans and line the bottoms with parchment paper.
• Whisk the soft white wheat flour, hard white wheat flour, cocoa powder, sugar, baking powder, baking soda, and salt together in a large bowl.2 cups freshly milled soft white wheat flour (229g),2/3 cup freshly milled hard white wheat flour (91g),3/4 cup unsweetened cocoa powder (64g),1 3/4 cups granulated sugar (372g),2 teaspoons baking powder (8g),1 1/2 teaspoons baking soda (7g),1 teaspoon salt (7g).
• In a separate bowl, whisk the eggs, sour cream, oil, buttermilk, and vanilla until smooth.3 large eggs,3/4 cup sour cream (180g),1/2 cup avocado oil (122g),1 cup buttermilk,2 teaspoons vanilla extract (10g).
• Add the wet ingredients to the dry ingredients and mix just until combined.
• Slowly pour in the hot water while mixing on low speed. Mix just until the batter is smooth and evenly combined.1/2 cup hot water.
• Let the batter rest for 10 minutes to allow the freshly milled flour to hydrate.
• Divide the batter evenly between the prepared pans.
• Bake for 24-27 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Start checking the cakes early to avoid overbaking. They're done when a toothpick inserted into the center comes out with a few moist crumbs attached, but no wet batter. If you see wet batter, continue baking for another minute or two before checking again.
• Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks and cool completely before frosting.

Frosting Directions

• Beat the softened butter for 2 to 3 minutes, until creamy and smooth.2 cups unsalted butter.
• Add the powdered sugar and cocoa powder gradually, mixing on low speed until incorporated.5 1/2 cups powdered sugar (651g),1 cup unsweetened cocoa powder (85g).
• Add the salt, vanilla, and heavy cream. Beat on high speed for 2 to 3 minutes, until light and fluffy.3/4 teaspoon salt (4g),1 tablespoon vanilla extract (15g),1/2 cup heavy cream (120g).
• If the frosting is too thick, add additional heavy cream 1 tablespoon at a time. If it is too thin, add a little more powdered sugar.