In a large saucepan bring cream to the beginning of a boil. Remove from cook top. Add chocolate (in chunks). Stir until completely combined. Cool to room temperature before filling cakes. Set aside to cool.
For Chocolate Cake: Preheat oven to 325 degrees F. Butter and flour cake pans of choice. Melt chocolate and set aside to cool to room temperature. Beat butter and brown sugar until fluffy (about 4 minutes on medium). Add eggs and vanilla and continue to beat until thick and creamy (about 6 minutes on medium). Add chocolate on low and mix until combined. Wisk dry ingredients together. Add 1/3 dry ingredients alternately with 1/3 sour cream beginning and ending with dry ingredients. Add boiling water and mix only for 30 seconds, scrape bowl and mix the rest by hand. Immediately pour into pans 2/3 full. Bake until tester comes out clean in center of cake, about 30 minutes for 9-inch round, more or less for other size cake pans. Cool for 1/2 hour before removing cakes from pans. Wrap in plastic wrap and cool in the refrigerator. When totally cold, unwrap cakes and fill with chocolate ganache.
For Orange Cake: Preheat oven to 325 degrees F. Butter and flour cake pans of choice With a zester, zest the orange part of the peel of a fresh orange but do not zest the white section of the peel. Measure 4 tablespoons. Combine yolks, 11/2 cups milk and extracts. Set aside. Combine dry ingredients in mixer and mix on low. Add 21/2 cups of milk, orange juice, butter and orange zest to dry ingredients and mix on low for 2 minutes. Beat on high for an additional 3 minutes. Turn mixer to low and add yolk mixture in 3 batches, mixing for 40 seconds on low each time. Fill buttered and floured cake pans 1/2 full. Bake until tester comes out clean and center springs back when lightly touched. Cool in pans for 20 minutes.
To assemble: Layer cake as follows: 1 layer chocolate cake, chocolate ganache, 1 layer orange cake, chocolate ganache, 1 layer chocolate cake. Frost as desired.