- Combine flour and powdered sugar; cut in butter until mixture resembles coarse crumbs.
- Press into the bottom of a greased 11-inch x 7-inch x 2-inch baking pan.
- Bake at 350 degrees F for 12 minutes.
- For filling, combine the first four ingredients in a bowl.
- Stir in rhubarb; pour over a warm crust. Bake at 350 F for 35-40 minutes or until wooden pick inserted in center comes out clean.
- Cool on wire rack.
- Serve warm if desired.
- Store in refrigerator.