Combine flour and sugar; cut in butter until crumbly. Press into a 13x9-in. baking pan. Bake at 350° for 10 minutes. Cool slightly.
For filling, blend flour and cream in a bowl until smooth. Add 1-1/4 cups sugar and egg yolks; mix well. Fold in vanilla and rhubarb. Pour into crust. Bake at 325° for 55-60 minutes or until a sharp knife inserted in the center comes out clean.
Meanwhile, make a meringue by beating egg whites until stiff. Add remaining sugar and beat again until stiff peaks form. Remove cake from oven; top with meringue immediately and broil lightly.