Combine all ingredients for crust and mix until crumbly. Pat half of the mixture into a 13x9x2 inch baking pan.
To prepare the filling, combine rhubarb, sugar, cornstarch and water in a medium saucepan and bring to a boil; reduce heat to low and continue to cook, stirring frequently, until mixture is clear. Stir in vanilla.
Pour filling over crust. Sprinkle with the remaining crumb mixture.
Bake for 20 minutes at 350°F. Allow to cool before slicing into serving sized bars.
Submitted by: CM