In a skillet over medium heat, soften the onions and garlic with the escargots in the oil. Season with salt and pepper. Add the zucchini and fennel seeds. Continue cooking for 2 minutes, stirring constantly. Deglaze with the Pastis and reduce until almost dry. Add the cream and broth mixture. Bring to a boil and simmer, stirring frequently, until the stew is thick. Adjust the seasoning.