Sally's Chocolate Birthday Cake

• For the Cake:
• 12 ounces unsalted butter (about 3 sticks; 340g)
• 12 ounces brewed black coffee, or black tea such as Assam (about 1 1/2 cups; 340g)
• 3 ounces Dutch-process cocoa powder (about 1 cup, spooned; 85g)
• 6 ounces finely chopped dark chocolate, roughly 72% (about 1 1/4 cups; 170g)
• 16 ounces light brown sugar (about 2 cups, packed; 455g)
• 1/2 ounce vanilla extract (about 1 tablespoon; 15g)
• 1 teaspoon (4g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 6 large eggs, straight from the fridge (about 10 1/2 ounces; 295g)
• 3 large egg yolks, straight from the fridge (about 1 1/2 ounces; 45g)
• 9 ounces all-purpose flour, such as Gold Medal (about 2 cups, spooned; 255g)
• 1 tablespoon (about 13g) baking soda
• 6 ounces finely chopped dark chocolate, roughly 72% (about 1 1/4 cups; 170g)
• 16 ounces light brown sugar (about 2 cups, packed; 455g)
• 1/2 ounce vanilla extract (about 1 tablespoon; 15g)
• 1 teaspoon (4g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 6 large eggs, straight from the fridge (about 10 1/2 ounces; 295g)
• 3 large egg yolks, straight from the fridge (about 1 1/2 ounces; 45g)
• 9 ounces all-purpose flour, such as Gold Medal (about 2 cups, spooned; 255g)
• 1 tablespoon (about 13g) baking soda 

Milk Chocolate Frosting
3 cups (24 oz) heavy cream
3 3/4 cups (20 oz) good quality milk chocolate, finely chopped
1/4 tsp kosher salt

1. Getting Ready: Adjust oven rack to lower-middle position and preheat to 350°F (180°C). Line three 9- by 2-inch anodized aluminum pans with parchment and grease with pan spray. (The cakes can be baked in 2-inch-deep pans, but they will dome more and rise less.)
   
2. For the Cake: Combine butter and coffee or tea in a 5-quart stainless steel pot or saucier over low heat. Once melted, remove from heat, then mix in cocoa and chocolate, followed by brown sugar, vanilla, and salt. Mix in eggs and yolks, then sift in flour and baking soda. Whisk thoroughly to combine.
   
3. Divide batter between prepared cake pans, about 23 ounces each. (If you don't have three pans, the remaining batter can be held at room temperature up to 90 minutes, though the rise will not be quite as high.) Bake until cakes are firm but your finger can still leave an impression in the puffy crust, about 30 minutes (a toothpick inserted into the center should come away with a few crumbs still attached).
4. Cool cakes directly in their pans for 1 hour, then run a butter knife around the edges to loosen. Invert onto a wire rack, peel off parchment, and return cakes right side up. Meanwhile, prepare the buttercream. 
    
   Frosting:
   

   In a 3 quart stainless steel pot, warm the cream over medium heat. When bubbling hard around the edges, pour over chocolate in the bowl of a stand mixer. Whisk by hand until smooth, stir in the salt, and set aside until no longer steaming. Cover and refrigerate six hours, or until thick and cold (45˚f) about 6 hours. Alternatively you can cool in an ice bath, stirring frequently, for about an hour.

   Whip with a whisk attachment on medium high until the frosting is thick and silky. (75 to 120 seconds). Use immediately.

   
   

   Assembly:

   Invert each pan onto a wire rack, and peel off the parchment. Trim the tops of the cake using a serrated knife. Place one layer cut side up on a serving plate or turntable. Cover with a cup of the frosting spreading evenly with the back of a spoon or offset spatula. Repeat with the second and third layers, cut side down. Finish the top and sides of the cake with the remaining frosting, and the decorations of your choice