For the Filling
In a small bowl, combine the brown sugar, cinnamon and allspice.
Cut in butter until crumbly; set aside.
For the Cake Batter
In a large bowl, cream butter and sugar until light and fluffy.
Add eggs, 1 at a time, beating well after each addition.
Beat in the sour cream, pumpkin and vanilla.
Combine the flour, cinnamon, baking soda and salt, then gradually add to creamed mixture.
Pour half of the batter into a greased 10" fluted bunt pan.
Sprinkle with reserved filling crumb mixture, then top with remaining batter.
Bake at 350 for 50 to 55 minutes or until a toothpick inserted in the center comes out clean.
Cool for 10 minutes before removing from pan to a wire rack to cool completely.
For the Glaze
Combine ingredients; drizzle over cooled cake.