Preheat oven to 350 degrees and spray a 9 x 13 inch dish with non-stick cooking spray.

In a large mixing bowl, make the cake batter by adding in 1/3 cup softened butter and 1/2 cup sugar. Cream together with a mixer until light and fluffy. Add in the egg and sour cream.

Mix until well combined.

Then mix in 1/3 of the milk mixture along with the vanilla. Then add in 1/3 of the flour along with the baking powder and salt just until combined. Continue alternating with another 1/3 of the milk followed by 1/3 cup of milk. Repeat agin with the remaining. Finish by mixing for about 2 minutes or until well combined.

Spread into the prepared 9x13 pan.

Then make the crumb topping, Add all of the ingredients into a bowl and mix to combine.

Then use your hands to crumble and sprinkle the mixture evenly over the top of the cake batter.

Bake at 350 degrees for 30 minutes, or until a toothpick inserted into the center comes out clean.

Cool completely. Serves 12-16.