Created by ellie on June 11, 2016
Step 1: Peel limes with a vegetable peeler; place rind and sugar in the bowl of a food processor; pulse until rind is broken up and mixed with the sugar. Transfer to a zip-lock bag; add 1/4 cup water and seal; pressing out any air. Let stand at room temperature 24 hours, massaging often. Strain through a fine sieve, pressing on the solids; discard solids.
Step 2: In a food processor, in batches, place watermelon and process until pureed; pour into a strainer set over a large bowl; stain, discard solids. Reserve 14 cups juice. Place 3 cups watermelon juice in ice cube trays (or a large ice mold or bowl) and freeze unit solid (8 hours).
Step 3: In a large pitcher mix the strawberry puree, vinegar, remaining 11 cups of watermelon juice, rind mixture, gin (if using) and tarragon. Refrigerate 2 hours or overnight.
Step 4: To serve add sparkling water to punch.
Step 5: Serve in ice-filled glasses with a frozen watermelon cube.