In a small saucepan, combine the sugar, and large rosemary sprigs and 1/2 cup water. Bring to a simmer and stir until the sugar is dissolved. Let simmer for 2 minutes. Turn off the heat and let the syrup sit for 30 minutes to cool.
Once cooled, discard rosemary sprigs. In a food processor, puree the pear and syrup. Spoon 3 tablespoons of the puree mixture into a champagne flute and slowly pour in the champagne. Stir gently and garnish with a small rosemary sprig.