Preheat oven to 350°F F; prepare Bundt pan.

Combine brown sugar, cinnamon and allspice in bowl. Rub in butter until crumbly; set aside.

Combine flour, cinnamon, baking soda and salt. In mixer bowl, cream butter and sugar until fluffy. Add eggs one at a time. Add pumpkin, sour cream and vanilla and mix well. Gradually add dry ingredients and mix well. Spoon half batter into pan; make well in center of batter and sprinkle streusel mixtute. Spoon remaining batter into pan and smooth top. Bake 50-60 minutes.Test for doneness. Cool in pan 20-30 minutes; turn onto serving; allow to cool completely.

Glaze with the powdered sugar and liquid adding liquid for desired thickness.