Heat the oil in a large nonreactive skillet over high heat. Add the fennel, onions, salt, and pepper and sautÈ for 2 minutes. Add the garlic and Pernod and stand back in case it flames.
Stir in the tomatoes and shrimp stock and bring to a simmer. Add the mussels and green onions, cover, and steam over high heat until all of the mussel shells have opened, for about 4 minutes.
Remove the mussels with tongs and let the broth cook for 2 minutes longer. Remove from the heat. Makes 3 cups broth.
To serve, arrange 10 mussels in each of 4 shallow bowls, and spoon 3/4 cup of the broth over them.
Yield: 4 first-course servings