Start by breaking down the fennel by removing the two outermost layers of the bulb. Trim the end, and cut the stalks off from where they protrude from the bulb. Remove some of the feathery fronds from the stalks and set aside for later. Roughly chop all the scraps and place them in a 2-quart pot. Pour the cold water over the fennel scraps, plunk in the whole clove of garlic (unpeeled is fine), and place over medium heat. Bring it to a gentle simmer, stir in a heaping ¼ t-spoon of kosher salt, and reduce the heat to low, simmering for 25 minutes uncovered. Once the broth is done, strain it into a large liquid measuring cup through a fine mesh sieve—you should have 5 cups left. Return to the saucepan, cover, and place over very low heat to just keep warm (with the parm rind, if using).