Preheat the oven to 350 degrees.
Grease and flour a 10-inch tube or bundt pan.
Drain the pumpkin by spreading over two layers of paper towels. Cover with two additional layers of paper towels and let stand for about 10 minutes. Scrape the drained pumpkin into a bowl.
Add the sugar, dark brown sugar and butter to a large bowl.
Beat at medium speed for 3 minutes or until well blended.
Add the eggs, one at a time, beating well after each.
Beat in the pumpkin and vanilla.
Measure the flour by lightly spooning into a dry measure cup and leveling with a knife.
Using a whisk or fork, combine flour, pumpkin pie spice, baking powder, baking soda and salt.
Add the flour mixture and buttermilk alternately to the sugar mixture, beginning and ending with the flour.
Pour the batter into the prepared tube or bundt pan.
Bake for 45 to 55 minutes or until a wooden pick inserted comes out clean.
Cool in pan for 10 minutes on a wire rack. Remove cake from the pan and cool completely on wire rack.
To prepare the glaze, combine all ingredients in a small saucepan over medium heat. Bring to a boil. Cook 1 minute or until thick, stirring constantly. Remove from heat and drizzle over cake.