2½ pounds rhubarb, washed and cut into 1-inch pieces
1 cup granulated sugar
1 cup water
1 medium lime, zested and juiced
10 cardamom pods, crushed
1 tablespoon whole celery seeds
1 tablespoon whole black peppercorns
Small pinch kosher salt
24 ounces soda water, chilled
Ice
Directions
In a large saucepan set over medium-high heat, combine the rhubarb, sugar, water, lime zest and juice, cardamom, celery seeds, peppercorns and salt. Bring to a boil, then reduce heat to a low. Simmer until rhubarb is very soft and smashes against the side of the pan easily, about 15 minutes. Strain the mixture through a fine-mesh sieve set over a medium bowl. Place the syrup in the fridge to chill completely (reserve the cooked rhubarb to serve with bacon or to use as a tart filling).
In a pitcher, stir the syrup with the soda water. Fill four glasses with ice and divide the rhubarb soda among the glasses. Garnish with celery leaves and a sprig of mint, if using.