In a mixing container, muddle the lemon and orange peels into the granulated sugar. (It will take several minutes--muddle until the peels have soaked up all the sugar.) Add the pear juice, syrup, bitters, lemon juice and gin. Add a single large block of ice (or several oversize cubes of ice) to the mixture and stir well. Divide between four glasses and top with sparkling wine.

*For the mulled spice syrup: In a saucepan over medium heat, bring 6 cups of demerara syrup (2:1) to a boil. Place 2 pieces star anise, 7 whole cloves and 2 cinnamon sticks in the center of a piece of cheesecloth. Gather the edges and secure with string to make a sachet. Add the sachet to the syrup and boil for 3 minutes. Transfer the mixture from heat and discard the sachet. Add 3 orange peels to the mixture, and let sit for 24 hours. Strain the syrup before using.