1. In a 5- to 6-quart pan over high heat, bring about 3 quarts water to a boil. Add half the spinach and cook until wilted, 1 to 2 minutes. Remove from water with a strainer and rinse under cold water until cool. Repeat to cook and cool remaining spinach. Squeeze or roll spinach tightly in a kitchen towel to remove as much water as possible.
2. In a food processor, whirl spinach, ricotta, eggs, cream, cheese, anchovies, salt, pepper, and nutmeg until well blended. Pour mixture into a buttered 2- to 2 1/2-quart soufflé or baking dish.
3. Bake on the middle rack of a 350° regular or convection oven until top looks solid when gently shaken, 45 to 50 minutes. Let cool 10 minutes.