1. 1. Heat the broiler. Put fennel seeds in a small, self-sealing plastic bag, and crush with a rolling pin. Add parsley, brown sugar, 3/4 teaspoon salt, and 1 teaspoon pepper to the bag, and shake to mix.
2. 2. Press the mixture onto the skinless side of the salmon. Broil salmon, skin side down, until it is no longer red in the center, about 8 minutes.
3. 3. Flake the fish with a fork. Meanwhile, in a large pot of boiling salted water, cook pasta according to package instructions until al dente, about 13 minutes. Reserve about 1/2 cup cooking water, and drain pasta. Return it to the warm pot, add spinach, and toss.
4. 4. In a bowl, mix together sour cream, lemon juice to taste, 1/2 teaspoon salt, and 2 tablespoons pasta water.
5. 5. Put pasta on plates, top with salmon, and drizzle with the sour-cream mixture. Or simply toss pasta and spinach in the pot with the salmon and the sour-cream mixture, adding pasta water as needed, and serve.
