How to Make It
In a medium saucepan, bring the rhubarb, sugar, orange peel and 1 cup of water to a boil. Simmer over moderately low heat, stirring occasionally, until the rhubarb breaks down, about 15 minutes. Let steep for 30 minutes. Strain through a fine-mesh sieve set over a medium bowl, pressing on the solids; discard the solids. Refrigerate the syrup until cold.
In a chilled glass, combine 3/4 ounce of the rhubarb syrup, the lemon juice, Bénédictine and orange bitters. Top with the sparkling wine and serve immediately. Use the remaining rhubarb syrup to make more cocktails.
A mixture of dry white wine and club soda can replace the sparkling wine.