*available seasonally at specialty produce markets and some supermarkets In a kettle of boiling salted water boil the fiddleheads for 4 minutes, or until they are crisp-tender, transfer them with a slotted spoon to a bowl of ice and cold water to stop the cooking, and transfer them to paper towels to drain. In the kettle boil the squash and the carrots for 3 minutes, or until they are crisp-tender, transfer the vegetables with the slotted spoon to the bowl of ice and cold water to stop the cooking, and transfer them to paper towels to drain. In the kettle boil the peas for 2 to 3 minutes, or until they are just tender, and drain them. In a large heavy skillet combine 2 tablespoons of the butter, the onions, the thyme, the bay leaf, 1/4 cup of the broth, and salt and pepper to taste and simmer the mixture, covered, for 5 minutes. Add the morels, halved lengthwise or sliced crosswise, and 1/2 cup of the remaining broth and simmer the mixture, covered, for 10 minutes, or until the morels are tender. Add the fiddleheads, the squash, the carrots, and the remaining 1/4 cup broth and simmer the mixture, covered, for 1 minute. Add the peas, the parsley, the mint, and the garlic, simmer the ragout, covered, for 1 minute, and stir in the remaining 2 tablespoons butter, cut into bits, stirring until the butter is just melted. Discard the bay leaf and season the ragout with salt and pepper. To clean fresh-picked fiddleheads: Snap off the crisp, bright green fiddlehead tops from ostrich ferns, leaving about 2 inches of stem attached. Rub off the dry brown casings by hand or put the fiddleheads in a wire salad basket and whirl the basket outdoors to remove the casings. Let the fiddleheads soak in a sink half full of cold water, changing the water several times to remove any grit or casing particles, and drain them. The fiddleheads keep, covered and chilled, for 1 week. Serves 6. Gourmet May 1992