Preparation

Cut the fennel trimmings and tops into chunks and put in a 4-quart saucepan. Add the thyme, star anise, Pernod, peppercorns, and 6 cups water. Bring to a simmer and cook until the fennel has softened and flavors have infused into the broth, about 30 minutes. Add the liquid from the oysters and strain through a fine-mesh strainer into a large measuring cup. You should have 6 cups broth. If you have less, add enough water to make 6 cups. Clean the saucepan, and return the broth to it. Add 2 tsp. salt and the saffron.

In a 5- to 6-quart Dutch oven or other heavy-duty pot, melt 4 Tbs. of the butter over low heat. Add the diced fennel, onion, and garlic. Cover and cook, stirring occasionally, until soft, about 10 minutes.

Reheat the fennel broth in the saucepan over low heat. Add the rice to the vegetables in the Dutch oven, and cook over medium-low heat, stirring frequently with a wooden spoon until the rice turns translucent with a white dot in the middle, about 5 minutes. Add the wine and cook over medium heat , stirring frequently, until the wine is completely absorbed, about 1 minute. Add 2 cups of the fennel broth and cook, stirring continuously, until most of the broth is absorbed, about 5 minutes. Continue adding the broth, 1 cup at a time, stirring continuously, until the broth is absorbed, 15 to 20 minutes more. The cooked rice should still have some texture and should not be mushy. If the rice is not cooked through and the broth runs out, add water 1/2 cup at a time and continue to cook, stirring continuously, until the rice achieves desired doneness. Remove from the heat and stir in the oysters, the remaining 2 Tbs. butter, parsley, and lemon zest. Divide among 4 shallow bowls and serve immediately with freshly ground black pepper, if desired.