Cream together 1/2 c. butter and 1 1/2 c. brown sugar.
Add 2 eggs. Blend well.
Combine 1 t. baking soda and 1 c. sour cream (or yogurt); add to creamed mixtures alternately with 2 c. flour. Stir in 2 c. chopped rhubarb, 1 t. vanilla and 1/2 c. chopped walnuts.
Pour in 9 by 13 baking pan.
In small bowl combine:
1/4 c. brown sugar
1/2 t. cinnamon
2 T. flour
Cut in 1/4 c. butter with pastry blender till crumbly. Sprinkle over cake batter.
Bake at 350 for 40 minutes.
Enjoy!! This is the cake that I've been bringing to church so regularly lately.