I always start by preheating my oven to 350°F and generously greasing every groove of my 12-cup bundt pan with butter and flour. This step matters more than people think, since a bundt cake that sticks can ruin all your hard work in seconds. I like to tap out the excess flour so there's no chalky coating left on the baked cake.
In a medium bowl, I whisk together the flour, pumpkin pie spice, baking soda, baking powder, and salt until they're evenly combined. Setting this aside lets the leavening agents distribute evenly, which helps the cake rise uniformly. I always give it one more quick whisk right before adding it to the wet mixture.
Using my stand mixer, I beat the butter, oil, brown sugar, and granulated sugar together until the mixture looks pale and fluffy, about two to three minutes. This step builds air into the batter, which keeps the finished cake from turning dense or heavy. Don't rush this part, since it really does affect the final texture.
Next, I add the eggs one at a time, beating well after each addition so the batter stays smooth. Then I mix in the full can of pumpkin puree and vanilla extract until everything looks fully combined. The batter will look thick and richly orange at this point, which is exactly what you want.
I add the dry ingredients to the wet mixture in two batches, mixing on low speed just until no streaks of flour remain. Overmixing at this stage can make the cake tough, so I stop the moment everything looks combined. The batter should be thick, almost like a heavy muffin batter.
I pour the batter into my prepared bundt pan, smoothing the top with a spatula so it bakes evenly. It goes into the oven for 60 to 65 minutes, and I test doneness with a toothpick inserted near the center. Once it comes out clean, I know the cake is ready to come out of the oven.
This part takes patience, but I let the cake cool in the pan for 15 minutes before inverting it onto a wire rack. It needs to cool completely, usually a few hours, before I even think about icing it. Icing a warm cake will just melt right off, so trust me on this one.
While the cake cools, I whisk together cream cheese, butter, powdered sugar, and cinnamon until smooth, then thin it out with a couple tablespoons of milk. I drizzle this over the cooled cake right before serving so it sets into those pretty ribbons down the sides. This icing is honestly what takes the cake from good to unforgettable.