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1
Prepare the matzo balls: Preheat the oven to 400u00b0F. Cut off the fennel stalks and reserve for another use (excellent for fish broths and stews). If there are some attractive feathery fronds, set aside about 2 tablespoons of them to garnish the soup. Quarter the bulbs and trim away the stems, the bottom hard core, and any tough parts. Choose a shallow baking pan just large enough to fit the fennel in one layer and put in 1 tablespoon of the oil. Add the fennel and toss until well coated. Roast the fennel until pale gold, about 20 minutes, then turn the fennel over and roast for 10 minutes longer. Stir in the broth, garlic, salt and pepper to taste, and 1/2 teaspoon of the thyme. Cover the pan with foil and cook for 35 to 45 minutes longer, or until the fennel is very soft. Remove the foil, stir, and roast for a few more minutes to evaporate most of the liquid. Transfer the fennel and garlic to a food processor and chop coarsely. Add the remaining 1/4 teaspoon of thyme, salt (it will need about 1 teaspoon), pepper to taste, and the fennel seeds, if using. With the machine on, add the remaining 1 tablespoon oil through the feed tube.
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2
Scrape the mixture into a large bowl. You need 1 cup of puree, so nosh on any extra. Whisk in the eggs, one at a time. Add the matzo meal and stir well. If you can form a lump into a very soft walnut-size ball (the batter will become firmer when you chill it), don't add any more matzo meal. If necessary, add just enough matzo meal to enable you to do so. Refrigerate for at least 2 or up to 4 hours so the matzo meal can drink in the liquid and seasoning.
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3
When ready to cook, bring 4 quarts water and 1 tablespoon of salt to a rapid boil in a large, wide, lidded pot. Dipping your hands into cold water if needed, roll the batter into walnut-size balls. When all the balls are rolled and the water is boiling furiously, turn the heat down to a gentle boil. Carefully slide in the balls one at a time and cover the pot tightly.
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4
Turn the heat down to a simmer, and cook over low heat for 30 minutes, without removing the cover. (They will cook by direct heat as well as by steam, which makes them puff and swell, and lifting the lid will allow some of that steam to escape.) Take out a dumpling and cut it in half. It should be light, fluffy and completely cooked through. If it isn't, continue cooking a few more minutes. Remove the balls gently with a skimmer or large slotted spoon-they are too fragile to pour into a colander.
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5
When the matzo balls are almost ready, start the soup: Bring the broth to a simmer in a large pot. Add the matzo balls, the mushrooms, and asparagus and simmer for about 5 minutes, until the vegetables are tender.
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6
Using a slotted spoon, transfer the matzo balls to shallow soup bowls and ladle the hot soup and the vegetables over them. Garnish with the reserved chopped fennel fronds.
