Servings: MAKES A 9-INCH TRIPLE-LAYER CAKE; SERVES 14 TO 16
Preheat oven to 350 degrees.
Grease three 9-inch cake pans. Line the bottoms with parchment paper and grease the paper.
Place the flour, sugar, cocoa powder, baking soda, cinnamon, and salt in a large mixing bowl and blend on low speed for about 30 seconds to mix.
Add the butter, sour cream, and unsweetened chocolate.
Continue to beat on low until thoroughly combined.
Scrape the bowl and raise the speed to medium; mix until light and fluffy, about 3 minutes.
Add the eggs one at a time.
Add the vanilla and mix to blend well.
Divide the batter evenly among the pans.
Bake until a toothpick or cake tester inserted in the center comes out clean, about 30 minutes.
Let the cakes cool in the pans for 5 to 10 minutes, then turn them out onto a rack and let cool completely.
To decorate the cake, place one layer bottom side up on a cake stand or dessert platter. Top with 2/3 cup of the Chocolate Glaze, spreading it to the edge of the cake. Set another layer on top and repeat. Set the top layer in place and pour the remaining glaze slowly over the center. Using a spatula, guide the glaze to the edges of the cake as you turn the stand so that the chocolate slowly spills over the sides and drips down the cake.
Place the bittersweet chocolate and half-and-half in a microwave-safe bowl and heat on the lowest setting or the defrost setting for 1 minute; stir well. Microwave for 30 seconds and stir again.
Repeat, if necessary, until the mixture is completely melted and smooth. Let cool until tepid; do not refrigerate.