Preheat oven to 350 degrees F. To prepare the cake, lightly coat a 10-inch tube pan with cooking spray and dust with flour.
Spread pumpkin over 2 layers of paper towels; cover with 2 additional layers of paper towels. Let stand about 10 minutes. Scrape drained pumpkin into a bowl.
Place granulated sugar, brown sugar and butter in a large bowl; beat with a mixer at medium speed 3 minutes or until well blended.
Add eggs, 1 at a time, beating well after each addition. Beat in pumpkin and vanilla. Whisk together flour and next 4 ingredients (through salt) in a bowl, stirring well.
Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture.
Spoon batter into prepared pan. Bake for 55 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes on a wire rack. Remove from pan, and cool completely on wire rack.
To prepare glaze, combine buttermilk and remaining ingredients in a small saucepan over medium heat; bring to a boil. Cook 1 minute or until thick, stirring constantly; remove from heat. Drizzle cake with glaze.
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