I first generously oil the Bundt or fluted cake pan so nothing sticks. Then I place chopped walnuts in the bottom — after baking, when I invert the cake, those walnuts become crunchy topping. Toasting them lightly beforehand enhances the flavor.
Next I mix together the boxed yellow cake mix and pumpkin pie spice. Then I add water, rum, oil, eggs, and pumpkin puree. I beat on medium speed until everything is well combined, making sure to scrape down the sides of the bowl to avoid unmixed pockets.
I pour the batter into the prepared pan and bake at 325°F (≈ 163°C) in the middle rack for about 25-30 minutes, or until the top springs back when touched or a toothpick comes out clean. Once out of the oven, I let the cake cool slightly, then loosen edges with a table knife and invert onto a plate. If using glaze, I mix powdered sugar, water and vanilla until creamy but pourable; then drizzle over the top and allow it to set a bit.