How to Make It
Using a Y-peeler, remove zest from one of the oranges; cut in half and squeeze juice into a large pitcher. Thinly slice second orange and add to pitcher.
In a small saucepan, bring sugar, 1 rosemary sprig, orange zest, and ¼ cup water to a simmer. Remove from heat and cover. Set aside for 5 minutes to steep; strain and discard solids.
Add the rosemary simple syrup to the pitcher along with the wine, elderflower liqueur, pear, and rosemary sprigs. Stir to combine. Top with club soda just before serving. Garnish with rosemary sprigs.
Make-ahead! Simple syrup can be made one week in advance.