Sift together flour, salt, cinnamon and 1/2 cup sugar. Cut in butter until crumbly. Sprinkle 1/2 of flour mixture in an 8 inch square pan and press down firmly. Mix rhubarb and lemon flavoring and 1 cup sugar. Spread over flour mixture in pan and sprinkle remaining flour mixture over rhubarb. Bake at 375 degrees F for 45-50 minutes. Serve with ice cream.