The macaroni keeps cooking after it leaves the pot, and that’s where a casserole can go from pleasantly tender to soft and swollen. In this Mac and Cheese Green Bean Casserole, the pasta gets a short head start in boiling water, then finishes in the oven under a creamy cheddar sauce. The green beans join the pot near the end, so they don’t have to endure the pasta’s full cooking time.
I like how the condensed cream of mushroom soup gives the cheese sauce a savory, casserole-style base, while sharp cheddar keeps it tasting like mac and cheese. A layer of French-fried onions goes on after the first part of baking, giving it time to turn golden without sitting in the oven from the start. After a short rest, the sauce settles around the pasta and beans, with crisp onions on top.
Kitchen Note
Wait to add the French-fried onions until the casserole has had its first bake. They need only a few minutes on top to turn golden, and adding them earlier risks a darker, less crisp topping.
Save this Mac and Cheese Green Bean Casserole for a bubbling cheddar bake with green beans and a golden French-fried onion top.
Why the Green Beans Get Only Four Minutes in the Pasta Pot
The beans need a shorter boil than the macaroni, even though they’ll finish baking together. Adding the cut green beans for the final four minutes of pasta cooking gives them a quick start without leaving them to soften through the entire boil. They’ll spend another stretch in the oven, surrounded by hot sauce, so keeping some firmness now helps them hold their shape on the plate.
The macaroni also benefits from stopping short of fully tender. Cook it for two minutes less than the package’s shortest al dente time; the oven is part of its cooking time, not just a way to warm the sauce. If the pasta already feels completely soft when you drain it, it has little room left before turning mushy in the finished casserole. Drain the pasta and beans together, then stir them into the sauce promptly so the noodles don’t sit and clump while you finish the other components.
This timing gives both parts a chance to land at the same place: tender macaroni and green beans that still have a little bite, held together by sauce that can cling instead of pooling at the bottom.
What the Mushroom Soup, Cheddar, and Fresh Beans Each Bring
- Condensed cream of mushroom soup — It brings a savory, creamy base that’s different from a plain milk sauce. Its thickness helps the cheese sauce coat the pasta and vegetables; swapping it out changes both the flavor and the body of the casserole.
- Sharp cheddar — The sharper flavor stands up to the pasta, green beans, and mushroom soup. Use a cheddar you enjoy eating on its own; the cheese is a major part of the sauce, and a mild version will make the finished dish taste less distinctly cheesy.
- Fresh green beans — Trimmed and cut into short pieces, they cook quickly and distribute through the casserole. Fresh beans give this version its tender-but-not-soft texture; large pieces are harder to eat alongside the macaroni.
- Elbow macaroni — Its small curved shape catches sauce in and around the pasta, making it a natural fit for a baked cheese casserole. Keep the package handy for its shortest al dente timing, since brands don’t all cook at the same rate.
- Whole milk and all-purpose flour — Together with the butter, they form the sauce base before the condensed soup and cheese go in. Whisking the flour into melted butter first helps disperse it, while gradually adding the milk makes it easier to keep the sauce smooth.
- French-fried onions — These bring a crisp, savory finish that contrasts with the creamy pasta underneath. Keep them for the topping rather than stirring them through, where they’d lose their crunch.
Build the Sauce and Bake Without Overcooking the Pasta
Give the Pasta and Beans Their Separate Timing
Heat the oven to 375°F and coat a 9×13-inch baking dish with nonstick cooking spray. Bring the water and kosher salt to a boil in a large pot, then add the elbow macaroni and cook for two minutes less than the package’s shortest al dente time. Add the green beans for the final four minutes, then drain both together. The pasta should still feel a little firm; it will continue cooking in the oven.
Cook the Flour Before Whisking in the Liquids
Melt the butter in a 4-quart saucepan over medium heat, whisk in the flour, and cook for one minute. Gradually whisk in the milk and condensed cream of mushroom soup, then add the dry mustard and black pepper. Bring the mixture to a simmer and cook, whisking, for four to six minutes until it thickens. Keep whisking across the bottom and corners of the pan so the sauce doesn’t catch while it reduces.
Melt the Cheddar Into the Sauce Off the Heat
Once the sauce has thickened, remove the saucepan from the heat before stirring in the cheddar. Stir until the cheese melts and the sauce looks smooth, rather than continuing to cook it over the burner. If the sauce looks thick in the pan, that’s fine; it will coat the drained pasta and beans when you combine them. Stir the sauce through the macaroni and green beans, then transfer everything to the prepared baking dish.
Finish with the Onions and Let the Casserole Rest
Bake the casserole uncovered for 15 minutes, then scatter the French-fried onions evenly over the surface. Return it to the oven for five to eight minutes, until the edges bubble and the onions turn golden. Watch the topping near the end, since it can go from golden to too dark quickly. Rest the casserole for 10 minutes before serving so the hot sauce settles around the pasta instead of running as soon as you scoop it.
Two Easy Swaps That Keep the Casserole’s Character
Make a Gluten-Free Version
Replace the elbow macaroni and all-purpose flour with gluten-free versions, and choose a gluten-free condensed cream of mushroom soup. Keep the listed quantities and use the pasta package’s shortest al dente time as your reference; gluten-free pasta brands vary, so check its texture before draining. The casserole keeps its creamy, cheesy character, though the pasta texture depends more on the brand.
Use Sharp White Cheddar
Swap sharp white cheddar for the sharp cheddar, keeping the same quantity. It melts into the same kind of smooth sauce but gives the casserole a paler color; choose a sharp variety rather than a mild one so the cheese flavor still comes through.
Storage and Reheating
- Refrigerator: Refrigerate leftovers promptly in a covered container and eat within 3 to 4 days. The pasta and beans soften, and the onion topping loses its crunch.
- Freezer: Freeze airtight for up to 2 months. Thaw overnight in the refrigerator; expect softer pasta and a less crisp topping after thawing.
- Reheating: Reheat covered in the oven until hot throughout, uncovering near the end to dry the topping a little. Microwave individual portions until steaming hot; avoid heating them longer than needed, since the pasta can dry out.
Questions That Come Up Before You Put This Casserole in the Oven
Mac and Cheese Green Bean Casserole
Ingredients
Equipment
Method
- Heat the oven to 375°F.
- Coat a 9x13-inch baking dish with nonstick cooking spray.
- Bring the water and kosher salt to a boil in a large pot.
- Add the macaroni and cook for 2 minutes less than the package’s shortest al dente time.
- Add the green beans for the final 4 minutes, then drain.
- Melt the butter in a 4-quart saucepan over medium heat.
- Whisk in the flour and cook for 1 minute.
- Gradually whisk in the milk and cream of mushroom soup.
- Whisk in the dry mustard and black pepper, bring to a simmer, and cook, whisking, for 4 to 6 minutes until thickened.
- Remove from the heat and stir in the cheddar until smooth.
- Stir the cheese sauce into the drained macaroni and green beans.
- Transfer the mixture to the prepared baking dish.
- Bake uncovered for 15 minutes.
- Scatter the French-fried onions evenly over the top.
- Bake for 5 to 8 minutes more until the casserole bubbles at the edges and the onions are golden.
- Rest the casserole for 10 minutes before serving.
