Can I use fresh green beans?
Yes. Blanch about 1 1/2 pounds trimmed fresh green beans in salted boiling water for 3 to 4 minutes, then drain and shock in cold water. Dry well, then proceed as written.
Can I use frozen green beans?
Absolutely. Thaw first and pat dry. Extra water is the enemy of a thick, creamy casserole.
Why is my casserole watery?
Usually it is one of three things: the beans were not drained well, frozen beans were added while still icy, or it was underbaked. Bake until you see bubbles around the edges and the center looks hot and glossy, not loose.
Can I make it ahead?
Yes. Mix and assemble the casserole without the final onion topping, cover, and refrigerate up to 24 hours. Let it sit at room temp for 20 to 30 minutes while the oven heats. Bake until bubbly, and if it still feels cold in the center, add 5 to 10 minutes. Then add the last of the onions and finish.
How do I make it more flavorful without changing the “classic” vibe?
Add 1 teaspoon soy sauce (or Worcestershire) and a good pinch of black pepper. It stays classic, just more “wait, why is this so good?”
Can I bake this in a 9x13-inch dish?
Yes, but you will want to double everything. The single batch is meant for an 8x8 or 9x9-inch dish. In a 9x13, it spreads too thin and can dry out.