Well butter a 12-cup (or larger) capacity bundt pan.
In a medium bowl, whisk together the flours, baking powder, baking soda, salt, cinnamon, cardamom, ginger, and allspice until well combined.
In a large bowl using a hand of stand mixer, beat together the brown sugar, butter and olive oil on medium-high speed until light and fluffy. Add the eggs one at a time, mixing in well. Add the pumpkin purée and sour cream, and mix until well combined, scraping the bottom and sides of the bowl as necessary.
Fold in the dry ingredients using a rubber spatula until well combined.
Pour the batter into the prepared pan, smooth the top and firmly tap the pan on the countertop a few times to release any large air bubbles. Cover the batter loosely with a clean kitchen towel and let rest for 15 minutes, or longer if you can. Then preheat oven to 350°F. Bake the cake until a tester inserted into the center comes out clean and the edges are starting to come away from the sides of the pan, 55 to 65 minutes, checking often.
Remove from oven and place the cake on a wire rack to cool for 20 minutes, then use the tip of a knife to loosen the edges and invert the cake onto the rack to cool completely before glazing.
Make the glaze: Once the cake is cool, melt the butter in a saucepan over medium heat. Cook the butter, occasionally scraping the bottom and sides of the pan with a rubber spatula until it turns a deep golden brown and smells nutty, for a few minutes.
Transfer butter to a heat-safe bowl, and let it cool slightly. Whisk in the powdered sugar and maple syrup until smooth. The glaze should be thick but pourable. If it’s too thin, add a bit more powdered sugar. If it’s too thick, add a few drops of water.
Transfer the cake to a serving platter and pour the glaze evenly over the top. Sprinkle with seeds if desired. Let the glaze set for a few minutes before slicing.