Tuna Mushroom Casserole

With its creamy sauce and layer of toasty bread crumbs, tuna noodle casserole is the ultimate comfort food. This recipe for tuna mushroom casserole elevates the basic one-dish meal with extra vegetables, a scratch-made sauce and Swiss cheese, making it a budget-friendly dish that strays from the norm. You’ll still use classic canned tuna and egg noodles, but this casserole also features green beans, onion and umami-rich mushrooms, plus a sprinkle of dill weed, which pairs beautifully with the creamy sauce. It’s practically a meal in itself, but you can’t go wrong with a leafy salad and dinner rolls on the side to stretch the it even more.

Ingredients for Tuna Mushroom Casserole

• Bouillon granules: Bouillon granules dissolve in boiling water more quickly than bouillon cubes. Most of these products are heavily salted, so look for a reduced-sodium or sodium-free version, or taste the broth before you add extra salt. Good chicken bouillon substitutes include homemade chicken broth or vegetable broth.
• Vegetables: To minimize shopping and speed up prep, this casserole uses a mix of fresh and frozen vegetables, including frozen cut green beans, onions, mushrooms, celery and garlic.
• Seasonings: Season the casserole lightly with dill weed, salt and pepper. To capture the full complexity of peppercorns, grind them directly into the vegetables.
• Sauce: The foolproof sauce consists of cornstarch, cold whole milk, shredded Swiss cheese and mayonnaise. It’s worth taking a few minutes to grate your own cheese; it will melt down more smoothly into the sauce than bagged grated cheese, which is coated in an anticaking agent.
• Egg noodles: Egg noodles have eggs mixed right into their dough, so they feel silkier and taste richer than other types of pasta.
• Canned tuna: This recipe calls for 12 ounces of tuna in water, so you may need multiple cans or pouches if you choose one of our top-rated tuna brands. Drain the tuna well and flake it into pieces for even distribution.
• Topping: Give tuna casserole its classic crunch by adding a buttery bread-crumb topping. You can make crumbs from scratch: Just tear a slice of day-old or toasted bread into pieces, pulse it in a food processor and then measure out what you need for the casserole topping.

Directions

Step 1: Dissolve the bouillon

In a large saucepan, bring the water and bouillon to a boil. Stir until the bouillon is dissolved.

Step 2: Simmer the vegetables

Add the beans, onion, mushrooms, celery, garlic, dill, salt and pepper to the broth and bring it to a boil. Reduce the heat, cover the pan and simmer until the vegetables are tender, about five minutes.

Step 3: Thicken the sauce

In a small bowl, combine the cornstarch and cold milk and whisk them until they’re smooth. Gradually add the milk mixture to the vegetables. Bring the mixture to a boil, then cook and stir it until it thickens, about two minutes.

Editor’s Tip: Cornstarch is one of the best thickeners for casseroles because it quickly creates a glossy sauce, but it must be handled correctly. Mix it into cold liquid until it forms a smooth slurry, and then add it slowly to the hot ingredients to prevent clumping.

Step 4: Build the casserole

Remove the vegetable mixture from the heat, then stir in the cheese and mayonnaise until the cheese melts. Fold in the noodles and tuna. Pour the mixture into a greased 2-1/2-quart baking dish.

Step 5: Top and bake the casserole

In a small skillet, brown the bread crumbs in the butter. Sprinkle them over the casserole. Bake the casserole, uncovered, in an oven set to 350°F until it’s heated through, about 25 to 30 minutes.

Editor’s Tip: Even though the bread-crumb topping will darken in the oven, it stays crisper if you brown the crumbs in butter first. If they start to become too dark while baking, cover the casserole loosely with aluminum foil until the final few minutes.

Tuna Mushroom Casserole Variations

• Change the vegetables: Replace the frozen green beans with frozen corn, peas or sweet peppers. Upgrade the mushroom type from common button mushrooms to more flavorful options, such as creminis, meaty portobellos, umami-rich shiitakes or oyster mushrooms.
• Keep everything fresh: Use fresh green beans, or substitute asparagus or zucchini. Replace the dill weed with fresh dill, thyme or oregano. Start the sauce with homemade chicken or vegetable broth instead of bouillon, and then fold in homemade egg noodles. You can even use fresh tuna: For safety, pan-sear it before flaking it into the casserole, or use grilled tuna steak or other cooked leftovers.
• Brown the vegetables: Before you simmer the vegetables in broth, brown them in a little butter or olive oil. This accentuates their flavor with caramelized notes that spread throughout the casserole as it bakes.
• Simplify the sauce: Add a can of condensed mushroom soup to make a quick, creamy sauce.

How to Store Tuna Mushroom Casserole

Let the tuna mushroom casserole cool completely before storing it. Pack leftovers in individual airtight containers or tightly cover the pan and store it in the refrigerator.

How long does tuna mushroom casserole last?

Refrigerated tuna mushroom casserole lasts three to four days. The bread crumbs will probably soften, but they might crisp up again in the oven. Still, an extra sprinkling of freshly toasted seasoned bread crumbs never hurts.

Can you freeze tuna mushroom casserole?

You can safely freeze tuna mushroom casserole, but the textures will change. Upon thawing, the milky sauce will likely separate, and the bread crumbs will be soggy. It helps if you freeze the casserole correctly: in portions that you only thaw and reheat once.

What’s the best way to reheat tuna mushroom casserole?

When reheating frozen tuna mushroom casserole, let it thaw overnight in the refrigerator before reheating it. For just-tender vegetables, smooth sauce and a crisp top, reheat the casserole in a baking dish in the oven. Take the casserole from the fridge while you preheat the oven to 350°, and then place the baking dish on the middle rack until the center of the casserole reaches an internal temperature of 165°. A microwave reheats casserole leftovers more quickly but also more unevenly. Use 30-second increments, stirring between them, for the best results.

Tuna Mushroom Casserole Tips

What can you serve with tuna mushroom casserole?

With its medley of vegetables, tuna mushroom casserole stands on its own as a meal. When choosing a side dish, stick to lightly dressed baby greens or a platter of crisp, fresh-cut vegetables. Barely seasoned cooked vegetables, such as lemon-pepper broccoli or air-fryer Brussels sprouts, also pair well with spoonfuls of creamy casserole. Choose contrasting sharp or strong flavors instead, such as the spicy radish and anise notes in shaved fennel salad. Leave room for dessert, too. Follow the heavy casserole with raspberry sorbet, chiffon cake or a plate of lemon bars.