Preheat the oven to 350 degrees F, and mist a 10-inch diameter tube pan with non-stick spray. Place the flour, brown sugar, cinnamon, baking powder, baking soda, and salt in a large bowl and whisk to combine.
Add the softened butter, mixing on medium speed, until the mixture resembles damp sand.
Add the eggs, one at a time, scraping the bottom and sides of the bowl with a silicone spatula after each addition.
Scrape the bottom and sides of the bowl with a silicone spatula, and stir in the milk and sour cream.
Mix on medium-high speed for about 90 seconds, to aerate the batter and develop the cake’s structure.
Layer 1/3 of the batter in the prepared pan, and top with half the pumpkin swirl mixture.
Repeat with another 1/3 of the cake batter and the remaining pumpkin swirl.
Top with the last of the cake batter, and sprinkle the crumb topping in an even layer on top.
Bake for 70 to 80 minutes, or until a bamboo skewer inserted in the thickest part of the cake comes out clean or with a few moist crumbs.
Cool completely, unmold, and drizzle with glaze.