Cook lima beans in boiling water until tender.
Melt 3 tablespoons butter in a saucepan and stir in flour.
Cook 1 or 2 minutes. Remove saucepan from heat and gradually add warm milk and ½ cup water. Return saucepan to the heat and continue cooking, stirring constantly, until sauce thickens. Season with salt, pepper and nutmeg and remove from heat. Add eggs slightly beaten and parmesan cheese. Stir cooked lima beans and correct seasoning.
Butter a medium size mold with remaining butter and flour it. Pour mixture and bake in preheated oven to 350°F ( 180°C) until flan is set.