Set your oven to 350°F. Lightly grease a 1.5-quart baking dish with butter or non-stick spray.
In a large bowl, whisk the cream of mushroom soup, milk, salt, and pepper until smooth.
1 can condensed cream of mushroom soup, ¾ cup milk, ½ tsp salt, 1 tsp ground black pepper
Add the drained green beans and half the French-fried onions. Stir gently so thebeans stay whole.
2 cans cut green beans, 1 cup french fried onions
: Pour the mixture into the baking dish. Spread it evenly and bake for about 25 minutes, until the sauce is hot and bubbling at the edges.
Removethe dish from the oven and sprinkle the remaining French-fried onions on top.
Return the casserole to the oven for another 5 minutes until the onions are golden brown and fragrant. Let it sit for a few minutes before serving to allow the sauce to thicken.