First, prepare the rhubarb syrup. Bring all of the rhubarb syrup ingredients to a boil in a small pot over medium heat. Reduce the heat to low and allow to simmer for 10 minutes, or until the rhubarb has softened a bit. Pour the contents of the pot into a blender or food processor and blend until smooth. Pour the syrup into a bowl and allow it to cool completely before covering it and placing in the refrigerator until chilled.

Once the syrup has chilled, you can start the margarita party. Take your serving glasses and, holding them upside down, dip the rims 1/4 inch deep into a shallow bowl of water. Then dip them into a shallow plate filled with the sea salt so that the salt sticks to the rim of the glasses. Set the glasses aside right-side up. To prepare the margarita, blend together all of the ingredients (except the sea salt) in a blender until the desired consistency is reached, then pour into the serving glasses. Garnish the rim of each glass with a rhubarb wedge rolled in sea salt and lay a sprig of rosemary across the top of each margarita. Serve and enjoy!