At Chicago restaurant Oriole, this chilled tisane is called Wholesome. Purchase osmanthus flowers from amazon.com.
Toast juniper berries, coriander seeds, osmanthus flowers, Szechuan pepper- corns, white peppercorns, and mustard seeds in a medium skillet over medium- low until fragrant, about 3 minutes. Let cool slightly. Transfer mixture to a mortar and pestle or spice grinder, and grind to a powder. Return spice mixture to skillet, and add 2 cups water. Bring to a boil over medium, and reduce heat to a simmer. Cook 10 minutes.
Pour mixture through a fine wire-mesh strainer into a heatproof measuring cup. Discard solids. Whisk sugar into tisane tonic. Let cool slightly. Cover with plastic wrap, and chill overnight.
To serve, fill a wine glass with ice, top with 1 1/2 ounces tisane tonic, a splash of club soda, and a splash of bitter lemon soda. Garnish with rosemary, edible flowers, and lemon and lime peel twists.
Store tisane tonic in an airtight container in the refrigerator up to 1 week.