Preheat oven to 350 and butter a 9 inch square pan. Sift flour, baking powder and salt in a bowl. Cream butter, sugar and orange zest together until fluffy. Add eggs one at a time, add vanilla and beat. Add the flour mixture alternating with the sour cream, beginning and ending with the flour mixture, craping down the sides of bowl occasionally. Fold in 1 cup of the cranberries. Spread the mixture into the prepared pan. Distribute the remaining 1 cup of the cranberries over the cake and sprinkle the crumb topping over the cranberries. Bake 45 to 50 minutes, test. Must be lightly golden and firm on top.
Vanilla Crumb Top: Combine first four ingrediants in a bowl, beat on very low speed until coarse crumbs, add vanilla and mix briefly. Distribute over the top of buckle.