In the bowl of a stand mixer, cream the butter and cream cheese with the sugars and pumpkin puree until smooth, about 5 minutes. Stop to scrape the sides and bottom of the bowl halfway between creaming.
Add eggs, one at a time, beating for 2 minutes after each.
Mix the dry ingredients (flour blend, pumpkin pie spice, and salt) in a medium bowl and slowly add into the wet ingredients just to incorporate. Finish folding in the flour mixture by hand with a spatula.
Scoop batter into a well-greased Bundt or tube pan and smooth top. Bake at 300° F for 1 hour and 30 minutes to 1 hour and 40 minutes, or until long skewer inserted into center comes out with a few crumbs stuck to it.
Remove from the oven and place on wire rack to cool completely in pan. Flip over and remove from pan onto cake plate or cake stand.
To make the glaze, whisk all glaze ingredients together until smooth. Slowly pour over cake and let drip down the sides. Add sprinkles on top if desired.