1. Preheat oven to 350 degrees. Generously butter a 9-by-13-inch cake pan. Line with parchment paper; butter lining. Dust with flour; tap out excess. Set pan aside.

2. Whisk together flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg, and cloves in a large bowl; set aside. Put butter and sugar in the bowl of an electric mixer fitted with the paddle attachment; beat on medium-high speed until pale and fluffy, 2 to 3 minutes. Add eggs, one at a time, beating well after each addition. Reduce speed to low; alternate between adding flour mixture and buttermilk, beginning and ending with flour. Add pumpkin, and beat until completely combined.

3. Pour batter into the prepared pan. Bake until golden and a cake tester inserted into center comes out clean, about 40 minutes. Let cool in pan on a wire rack 15 minutes. Unmold; peel off parchment. Let cool completely on rack, top side up.

4. Set cake and rack on a baking sheet lined with parchment paper. Pour warm chocolate glaze over cake. Using a small offset spatula, gently smooth glaze over top of cake, letting it drip down sides. Let stand at room temperature, or refrigerate until set. Arrange 6 headstones on top; serve with the remaining.