Mix flour, oatmeal, brown sugar and butter until crumbly. Press half into greased 23 cm pan. Add rhubbard, cut in 1 cm pieces. Combine sugar, cornstarch, water and vanilla; cook till thick and clear. Pour sauce over rhubarb. Top with other half crumb mixture. Bake at 180ºC for 45 minutes. [Flanagan Parent-Teacher Club Cookbook GEnie/D.WEISSGERBE AOL/Rik W]