Add rhubarb and sugar to a small pot, and fill pot with just enough water to cover the rhubarb. Bring to a boil, then lower heat to medium. Cover, and simmer until the rhubarb stalks begin to fall apart.
Strain sugar-water off of the rhubarb into a container, reserving rhubarb for another recipe if desired. Allow rhubarb syrup to cool to room temperature. (If desired, put syrup in the fridge to speed cooling process.)
Pour 1 oz rhubarb simple syrup into a champagne flute or coupe cocktail glass. Top syrup with champagne until the glass is full. Serve immediately.
*Faster Cook Time: The Rhubarb Simple Syrup can be made ahead of time to shorten the recipe time to 1 minute.