Making the orange juice mixture: Put the sugar, cloves, cardamom, bay leave, star anise, lemongrass and 1/2 cup water in a pot and bring to a boil. Reduce the heat and simmer until the spices release their flavor, about 5 minutes. Remove from the heat and cool for another 5 minutes. Combine the spice mixture and orange juice in a bowl, and refrigerate for 30 minutes. Once chilled, strain and discard the spices.
Take 4 champagne flutes. Put 4 lemon balm leaves into each glass and bruise the leaves with a muddler. Pour 1/2 cup juice and 1/2 cup prosecco into each glass. Decorate with fresh orange slices.
For an optional garnish, preheat the oven to 225 degrees F. Take 1 orange and slice it thinly. Put the slices on a sheet pan lined with parchment. Dust each slice with powdered sugar and transfer the sheet pan to the oven. Dehydrate the orange slices for about an hour. Put the dehydrated slices on each glass for crunch.