Combine rhubarb and 1/2 cup of sugar and set aside. Mix flour, 1 1/2 cups of sugar, oil, sour milk, egg, baking soda, cinnamon and vanilla. Add the rhubarb and sugar mixture. Stir until well blended. Pour into greased and floured 9x13 pan.
Bake at 350°F for 1 hour until done.
Combine the 5 Topping ingredients and cook for 3 minutes. Pour topping over cake while still warm.