Kansas: a featured recipe

In an older Taste of Home magazine I found an article about Kansas and the wheat grown there. In it was a recipe for this Rhubarb Coffee Cake.
I altered it slightly and it was SO good!!!! I would highly recommend it! :)

Rhubarb Coffee Cake

1/2 cup butter, softened

1/2 cup packed brown sugar

1/4 cup sugar

1 egg

1 teaspoon vanilla

1-1/4 cups flour

3/4 cup whole wheat flour

1 teaspoon baking powder

1/2 teaspoon baking soda

1/4 teaspoon salt

1/4 teaspoon ground cinnamon

1 cup kefir or buttermilk

2 cups chopped fresh or frozen rhubarb

Topping:

1/4 cup packed brown sugar

1-1/2 teaspoons ground cinnamon

1/2 cup slivered almonds or chopped walnuts

In a mixing bowl, cream butter and sugars. Add egg and vanilla; beat until fluffy. Combine flours, baking powder, baking soda, salt and cinnamon; add to creamed mixture alternately with kefir, mixing well after each addition. Stir in rhubarb. Pour into a greased 13-in. x 9-in. baking pan. Combine the topping ingredients; sprinkle evenly over batter. Bake at 350 degrees for 35 minutes or until a wooden pick inserted near the center comes out clean. Serve warm or at room temperature.