In a saucepan, combine sugar, flour, cinnamon and salt. Stir in water; add butter. Bring to a boil; cook and stir 1 minute. Remove from heat. Add vanilla and, if desired, enough food coloring to tint sauce a deep pink; set aside.
For dough, in a medium bowl, combine flour, sugar, baking powder and salt. Cut in butter until mixture resembles coarse crumbs. Add milk and mix quickly. Do not. Gather dough into a ball and roll out on a floured surface into a 12-in. x 9-in. x rectangle. Spread with softened butter; arrange rhubarb on top.
Combine sugar and cinnamon; sprinkle over rhubarb. Roll up from the long side and place on a cutting board, seam side down. Cut roll into 12 slices. Arrange slices cut side up in a greased 13-in. x 9-in. baking dish. Pour sauce over. Bake at 350° for 35-40 minutes or until golden brown. Yield: 12 servings.