Ingredients
3 cups water
2 cups plus 2 tablespoons sugar
1/2 vanilla bean, split and seeds scraped, pod reserved
1 strip (2 inches) lemon zest
1 1/2 pounds rhubarb, cut into 1 1/2-inch pieces
4 large egg yolks
3 tablespoons elderflower liqueur, such as St-Germain, or any other sweet, floral liqueur
Preparation
Prepare an ice-water bath. Bring water, 2 cups sugar, the vanilla seeds and pod, and lemon zest to a boil in a wide, shallow saucepan. Stir. Reduce heat. Simmer for 10 minutes. Add rhubarb, and simmer gently until just tender, 3 minutes. Transfer to a bowl set in ice-water bath. Let cool completely. Divide among 4 bowls.
Whisk together remaining 2 tablespoons sugar, the egg yolks, and the elderflower liqueur in a double boiler or a heatproof bowl set over a pan of simmering water. Cook, whisking constantly, until sabayon is tripled in volume, frothy, and warm to the touch, 6 to 8 minutes. Serve immediately over rhubarb.
