In a bowl, cream butter and sugar until fluffy. Add eggs, one at a time, beating after each addition. Add vanilla; mix well.
In a bowl, whisk together flour, baking powder, baking soda, and salt. Add to creamed mixture alternately with sour cream. Fold in rhubarb. Spread in a greased 9 x 13 baking dish.
For topping, in a bowl, combine brown sugar, flour and cinnamon. Cut in butter until mixture resembles coarse crumbs, sprinkle over batter.
Bake at 350° until a toothpick inserted in center comes out clean, 45-50 minutes. Cool on a wire rack.
Notes
This recipe can be changed by substituting fresh peaches or fresh apples instead of rhubarb. Reduce sugar to 1 cup if changing fresh fruits.