We hollowed out a ten-pound blue Hubbard squash to use as a tureen for the soup.
Place porcini mushrooms in a bowl; add hot water to cover (about 1 1/2 cups). Let stand until mushrooms are soft, 10 minutes.
Meanwhile, melt butter in a large pot over medium heat. Add onions and cook, stirring often, until soft and translucent. Add thyme, 1 teaspoon salt, and 1/2 teaspoon pepper.
Stir in barley and cook until it begins to brown and smell sweet.
Lift mushrooms out of soaking liquid. Strain liquid through a cheesecloth-lined sieve and set aside. Chop mushrooms coarsely and add to barley mixture. Add 1/2 cup Madeira, raise heat to medium-high, and cook until liquid is nearly evaporated. Reduce heat to medium, add reserved soaking liquid, and cook until liquid is almost completely reduced.
Stem Swiss chard. Chop stems into 1/2-inch pieces; add to barley mixture. Chop leaves into 1/2-inch pieces and set aside.
Drain tomatoes and add tomato juice to barley along with vegetable stock. Seed and core tomatoes, cut into 1/2-inch dice, and set aside. Cut squash in half lengthwise and remove seeds with a spoon. Remove skin and cut flesh into 1/2-inch cubes. Add squash, 1 teaspoon salt, and remaining 1/2 teaspoon pepper to soup. Let simmer about 50 minutes, skimming foam occasionally. Add chopped tomatoes for last 20 minutes of cooking time.
Just before serving, add chopped Swiss chard leaves and remaining 1/2 cup Madeira. Cook until chard is just tender, 2 minutes. Add remaining 1 1/2 teaspoons salt and serve.