2. Melt 1 tablespoon butter in an 8- or 10-inch skillet over medium heat. Add the onions, sprinkle with the sugar, and season with a little salt and freshly ground pepper. Cover and cook over a low heat until the onions are lightly browned and nearly tender, about 12 minutes. Give the pan a shake every few minutes. Add the fennel and continue cooking, covered, until tender.
3. In another skillet, melt 2 tablespoons butter. Add the walnuts and cook over low heat, occasionally giving the pan a shake, until they're golden, 12 to 15 minutes. Add the stock and the herbs. Simmer, covered, until the liquid is reduced to a few tablespoons of syrupy juices. Taste for salt and pepper then combine them with the onions and fennel.
4. Boil the Brussels sprouts in salted water until tender, then add them to the mixture. Add the walnut oil and additional fennel greens, gently stir everything together and serve.
Excerpted from Vegetarian Cooking for Everyone by Deborah Madison (10th anniversary edition, Broadway Books, 2007). Copyright 2007 by Deborah Madison.
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