In a large saucepan, melt the butter and saute the onion until translucent, 3 to 4 minutes. Add the soups, milk, and half-and-half. Add the crabmeat and bring just to a boil. Add the sherry and salt and pepper, to taste. Serve immediately. Or allow to cool to room temperature, then refrigerate or freeze immediately in plastic microwavable reusable containers with lids.