Prepare oven and pans: Preheat oven to 350°F Grease and flour two 9-inch round baking pans; set aside.
Combine ingredients: In an extra-large bowl combine buttermilk, water, oil, sugar, eggs, baking soda, and salt. Using a large wire whisk, whisk until well combined. Add flour and cocoa powder; whisk vigorously until smooth. Divide batter between prepared pans.
Do the touch test: Bake for 30 to 35 minutes until top springs back when lightly touched in center. Cool in pans on a wire rack for 10 minutes. Remove from pans and cool completely.
Prepare pumpkin cream filling: In a medium bowl whisk together cream cheese, pumpkin, sugar, and cinnamon until thickened. Place one cake layer on plate. Spread filling over top. Top with second cake layer.
Make chocolate glaze: In a saucepan bring whipping cream just to boiling over medium-high heat. Remove from heat. Add chocolate (do not stir). Let stand 5 minutes. Stir until smooth. Cool 15 minutes or until slightly thickened. Pour over cake, allowing glaze to drip down sides. Chill until set, about 30 minutes. Top with desired toppers. Makes 14 servings.