Best Chocolate Cake

Preheat the oven to 350°F. Line two 8 by 2-inch cake pans** with parchment rounds and spray evenly with nonstick cooking spray.
In a small heatproof bowl, whisk together the cocoa powder and espresso powder. Pour the boiling water over mixture and whisk gently until smooth. Set aside to cool completely.
In a large bowl, either sift*** or whisk together the flour, salt, and baking soda. Add brown sugar and use your hands to break up any clumps until the mixture resembles sand.
In a separate small bowl, whisk together the sour cream, oil, eggs, and vanilla until smooth. Make a well in the center of the dry ingredients and pour in the wet ingredients. Starting in the center, use a whisk to slowly pull the dry ingredients into the wet until mostly combined. The batter may be slightly lumpy.
Add the cooled cocoa mixture and whisk until the batter is smooth and evenly combined.
Divide the batter evenly between the prepared pans (about 740 grams per pan). Tap each pan firmly on the counter a few times to pop any air bubbles. Bake for about 32 to 35 minutes, or until a toothpick or cake tester comes out with moist crumbs attached.
Cool in the pans for 30 minutes, then (if needed) run a thin knife around the edges and remove to a wire rack to cool completely.

If your cake has domed at all, level with a serrated knife or cake leveler until it is flat.
Place one cake layer on a cake turntable or cake stand. Place strips of parchment paper under the cake to prevent a frosting mess.
Spread a generous, even layer of frosting over the top, pushing it out over the edges slightly. Place the second layer upside down onto the frosting so the top of the cake is nice and flat.
Using an offset spatula, spread the remaining frosting evenly all over the cake, smoothing the edges. Serve immediately, or cover and refrigerate for up to 2 days. Let sit at room temperature for an hour before serving.