Sourdough Coffee Cake

This recipe is one I came up with last summer. I am sharing it now for the Sourdough Surprises challenge of the month.  
This is a really tasty coffee cake. I could not taste any of the sourdough flavor in the finished cake, but it still has the health benefits that sourdough offers.

Sourdough Coffee Cake

1/2 c. sourdough starter
1/2 c.+2 T. kefir or buttermilk 
1 1/2 c. whole wheat flour
1/2 c. sugar
1/4 c. melted butter
1 egg
3/4 t. salt
3/4 t. baking soda

Strussel

1/2 c. sugar
1/4 c. whole wheat flour
2 t. cinnamon
3 T. melted butter

 Mix starter, buttermilk and flour. Cover, and rest overnight. 
In the morning mix together the strussel ingredients in a bowl. 
To the flour/kefir mixture add the egg, butter, sugar, and salt. Beat until the batter starts to come together and resembles cake batter.
Sprinkle baking soda over the batter and stir briefly, but, well. 
Pour 1/2 of the batter into a greased 8x8 inch pan. Sprinkle 1/2 of the strussel over the top. Pour in the remaining batter and top with the remaining strussel. 
Bake at 350* F. for 40-45 minutes.