3. Wipe out the sauté pan and return it to the stove over medium heat. Melt the butter, then add the flour and cook, stirring, for 1 minute, to make a light roux. Add 1⁄2 cup stock, cream, and the reserved cooking liquid from the greens, and continue to cook for about a minute longer, or until the mixture thickens. Stir in the Parmesan and ricotta cheeses and cook for another minute. Transfer this to the bowl with the reserved greens. Mix well, then pour it into the buttered baking dish and top evenly with the breadcrumbs and mozzarella. Bake in the oven for 20 minutes, or until it begins to brown. Remove from the heat and cover with foil to keep warm.