1. With the stem side up, cut a 3-inch circle from the top of the melon (removing the flesh from the plug and reserving the plug to use as a lid). If necessary, cut a sliver from the bottom of the melon so it stands upright.

2. Using a slotted spoon, scoop out the red flesh from the melon and place it in a large bowl (make sure to scrape all of the flesh out until only traces of pink remain). Place the hollowed-out shell in the freezer for at least 1 hour to set.

3. Meanwhile, use your hands to crush the melon flesh as much as possible. Strain through a fine-mesh strainer into another bowl and set the juice aside.

4. Transfer the melon solids to a food processor or blender and puree for 2 minutes. Strain the puree into the reserved juice. There should be about 5 cups of liquid.

5. Place the sugar into a microwavable bowl and stir in 2 cups of watermelon juice (refrigerate or freeze the remaining juice for future use). Microwave on high for 5 minutes, then stir to ensure that the sugar is completely dissolved. Let the syrup cool to room temperature or hasten the process by placing the bowl in a larger bowl filled with ice water.

6. Place the strawberries, raspberries, cherry preserves, bitters, if using, and 1 cup of watermelon syrup in a food processor or blender and puree until the fruit is smooth, 3 to 4 minutes.

7. Pass the puree through a fine-meshed strainer (preferably a chinois) into a tall plastic pitcher.

8. Carefully place the whole, raw egg into the puree. If it floats to the top enough to reveal a quarter-sized circle of shell, there is enough sugar in the puree for the sorbet to freeze properly into tiny crystals. If the egg is not visible, remove it and stir in more watermelon syrup by half-cupfuls until the egg, returned to the puree, floats to the top. (The egg can be rinsed off and returned to the refrigerator.)

9. Freeze the sorbet in an electric ice cream freezer according to the manufacturer's directions (depending on the size of your ice cream freezer, you may have to do this in batches).

10. When the sorbet is very slushy, transfer it to a 3-quart plastic food storage container. Stir in the chocolate chips. Place a sheet of plastic wrap directly on the surface of the sorbet and freeze the container for about 2 hours to "ripen" but not to freeze solid.

11. Spoon the sorbet into the hollowed-out, frozen watermelon shell, leaving a half-inch of empty space at the top to allow for expansion. Cover the hole with the reserved plug and freeze the melon overnight. (Freeze any remaining sorbet in a separate container.)

12. To serve, remove the plug and scoop out the sorbet.