Preheat oven to 350F (175C) and thoroughly grease and flour a 12-cup bundt pan (tap out excess flour). Set aside.
In a large mixing bowl, combine butter, sugars, and spices (cinnamon, ginger, allspice, nutmeg) and use an electric mixer to cream together until light and fluffy and well-combined (about 2-3 minutes on high speed).
Add eggs, one at a time, stirring very well after each addition (about 30 seconds after each addition on high speed).
Stir in pumpkin, sour cream, and vanilla extract.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
With mixer on low-speed or, stirring with a spatula, gradually stir dry ingredients into wet (I do this in 3-4 parts).
Pour batter into greased bundt pan and bake for 60 minutes or until a wooden skewer inserted into the thickest part comes out clean or with moist crumbs.
Allow to cool in pan for 30 minutes then carefully invert onto cooling rack and allow to cool completely before icing.
Cream Cheese Glaze
In a microwave-safe bowl, stir together cream cheese and butter until smooth and creamy.
Gradually stir in powdered sugar until combined, then stir in vanilla extract.
Transfer bowl to the microwave and microwave in 5-10 second intervals, stirring in-between, until mixture is melty and pourable.
Drizzle or pour over bundt cake. Allow glaze to firm before slicing and serving.