For a simple start, use HOME MADE onion rings, instead of the canned. People will rave! Also, DO NOT USED CANNED GREEN BEANS. I have never tested the following, but here are a couple more. Now, you’re ready to kill me! 
From Martha:
You would be able to simplify this a lot, but it seems like a pretty good place to start:
WORLD’S BEST GREEN BEAN CASSEROLE
Adapted from Cook’s Illustrated, November-December 2006
Hands-on time: 30 minutes
Time to table: 45 minutes
Serves 8 in small-ish servings for a big dinner
BEANS
2 quarts water
1 tablespoon table salt (salt is key to the flavor so don’t skimp; if you don’t have table salt, use twice as much as the relatively ‘less salty’ kosher salt or sea salt)
1 pound fresh green beans, ends snapped, snapped into bite-size pieces
Bring the water to boil in a large pot or Dutch oven. While it comes to a boil, prep the beans. Fill a large bowl with ice water. Add the salt and beans to the boiling water. Cover and cook for 6 minutes or until crisp-tender and still bright green. Drain beans in a colander, then plunge into ice water to stop the cooking. Drain a bit in the colander again. Place a double layer of paper towels on a baking sheet, arrange beans in single layer to dry, top with a double layer of towels. (If doubling/tripling the recipe means cooking the beans in batches, start each batch with fresh water; at minimum, re-salt the water with each new batch. Don’t skip the drying process.)
MUSHROOMS & SAUCE
8 ounces baby portabella mushrooms (I like the color of the brown portabella but taste-wise, they’re the same as white button mushrooms)
1 tablespoon unsalted butter
1 tablespoon fresh garlic, minced
Kosher salt to taste
Fresh pepper to taste
1 1/2 tablespoons flour
3/4 cup chicken stock
1 tablespoon dry sherry
3/4 cup half & half or heavy cream (don’t use fat-free half-n-half, it won’t thicken)
Salt & pepper to taste
Clean the mushrooms; break off and discard the stems. (Better yet, use the stems to make a night-before-Thanksgiving mushroom soup.) Break the mushroom tops into pieces. (Breaking the tops is important to the texture for slicing them with a knife makes the mushrooms more like the ones in canned soup.) Melt the butter in a skillet til shimmery. (To save a pan, use the pot used for cooking the beans.) Add the mushrooms, garlic, salt and pepper. Stirring often, cook til mushrooms begin to soften and exude their liquid, about 6 minutes. Stir in flour and cook a minute. Add the chicken stock, sherry and bring to a simmer. Add the half & half, simmer til sauce thickens, about 10 - 15 minutes. Taste and adjust the seasonings. Stir in the cooked beans til they’re evenly distributed throughout the sauce.
TOPPING (the quantity below is half what the inspiring recipe used; the full amount seemed way over the top to me, plus you can see from the picture, the topping isn’t in the least bit skimpy)
1 slice good whole grain bread (I used this whole grain bread, the version without beets)
1 tablespoon unsalted butter
1/2 a 2.8 ounce can of French fried onions
1/8 teaspoon table salt
1/16 teaspoon freshly ground black pepper
In the food processor, process the bread, butter and seasonings in about 10 quick pulses. Stir in the onions – but don’t process. If making ahead, transfer to a storage container and refrigerate.
COOKING RIGHT AWAY Preheat oven to 425F. Transfer hot bean mixture to a greased quiche pan or baking dish. Top beans with topping and bake for 15 minutes.
COOKING LATER Transfer bean mixture to a greased quiche pan or baking dish, cover with plastic wrap and refrigerate. Return to room temperature. Remove plastic wrap. Heat in 425F oven for about 10 - 40 minutes until hot and bubbly. (Ten minutes works okay for a shallow wish like a quiche pan. Allow more time for a deeper dish.) Add topping and bake for another 15 minutes.
TIMING MULTIPLE BATCHES For larger gatherings, I’ve doubled and tripled this recipe. The prep is easy enough but the timing changes since it takes longer to bring the casserole to room temperature (allow 3 hours for a triple batch) and longer to heat it through (allow at least 30 - 40 minutes for a triple batch, especially one prepped in advance or not quite at room temperature).
TO PREP AHEAD
DAY BEFORE Make the entire casserole but don’t apply the topping.
BEFORE DINNER Bring to room temperature. Bake for 10 - 40 minutes at 425F. Apply topping and bake for another 15 minutes.
NUTRITION ESTIMATE
Per Serving: 138 Cal (54% from Fat, 12% from Protein, 33% from Carb); 4 g Protein; 9 g Tot Fat; 5 g Sat Fat; 12 g Carb; 3 g Fiber; NetCarb8; 54 mg Calcium; 1 mg Iron; 218 mg Sodium; 16 mg Cholesterol; Weight Watchers 2 points