Blueberry Buttermilk Coffee cake

1/2c butter
1 1/3c. sugar
2 eggs
1tsp. vanilla
2c. buttermilk
4c. flour
3tsp. baking powder
1tsp. baking soda
1tsp. salt
2c. blueberries

Topping:
2/3c. flour
2/3c. sugar
6T. butter

Preheat oven to 350 degrees. Grease and flour a 9x13 pan. Sift together the flour, baking powder, baking soda and salt. In large bowl cream butter and sugar until light and fluffy. Add the eggs, one at a time. Stir in vanilla. Add the flour mixture alternately with the buttermilk. Mix until just incorporated. Carefully stir in blueberries. Pour into prepared pan. For the topping; combine the flour and sugar. Using pastry blender or 2 knives, add in the butter until mixture is crumbly. Sprinkle over cake. Bake for 45-60 minutes, or until toothpick comes out clean. Allow cake to cool. Refrigerate leftovers. ( I add 4T. flour for high altitude.)