This vegetable medley casserole combines tender vegetables with a creamy, lightly seasoned sauce and a golden Swiss cheese topping. It’s a comforting side dish that works with fresh or frozen vegetables, and a brief precook helps keep the casserole flavorful rather than watery.
Ingredients
- 2 tablespoons unsalted butter, plus a little for greasing the dish
- 1 medium yellow onion, finely chopped (about 1 cup)
- 2 medium carrots, peeled and cut into small dice (about 1 cup)
- 2 cups broccoli florets, cut into bite-size pieces
- 1 cup cauliflower florets, cut into bite-size pieces
- 1 cup frozen peas, thawed
- 3 tablespoons all-purpose flour
- 1 cup whole milk, warmed
- ½ cup low-sodium vegetable broth
- ½ teaspoon fine salt, plus more to taste
- ¼ teaspoon black pepper
- ¼ teaspoon dried thyme
- ¼ teaspoon ground mustard
- 1½ cups shredded Swiss cheese, divided
- ½ cup plain breadcrumbs
- 1 tablespoon olive oil
Instructions
- Heat the oven and prepare the vegetables. Set a rack in the middle of the oven and preheat it to 375°F (190°C). Lightly butter a 2-quart baking dish. Bring a large pot of salted water to a boil. Add the carrots and cook for 3 minutes; add the broccoli and cauliflower and cook for 2 minutes more. The vegetables should be just starting to soften, not fully tender.
- Drain thoroughly. Drain the vegetables in a colander and let them steam-dry for a few minutes. This step is important: excess water can thin the sauce and make the finished casserole soupy. Add the thawed peas and set the vegetables aside.
- Cook the onion. Melt the butter in a medium saucepan over medium heat. Add the onion and cook for 4 to 5 minutes, stirring occasionally, until soft and translucent. Avoid browning it heavily, which can overpower the gentle flavor of the Swiss cheese.
- Make the sauce. Sprinkle the flour over the onion and stir constantly for about 1 minute to cook away its raw taste. Gradually whisk in the warm milk, followed by the broth. Keep whisking until smooth, then cook for 3 to 5 minutes, stirring often, until the sauce thickens enough to coat a spoon.
- Season and add cheese. Stir in the salt, pepper, thyme, and ground mustard. Remove the pan from the heat and mix in 1 cup of the shredded Swiss cheese until melted. Taste the sauce and adjust the seasoning if needed; remember that cheese adds salt, so taste before adding much more.
- Assemble the casserole. Fold the drained vegetables into the cheese sauce until evenly coated. Spoon the mixture into the prepared dish and spread it into an even layer.
- Add the topping. Toss the breadcrumbs with the olive oil, then scatter them evenly over the casserole. Sprinkle the remaining ½ cup Swiss cheese on top. The oil helps the crumbs brown, while the cheese makes a savory, lightly crisp surface.
- Bake and rest. Bake uncovered for 25 to 30 minutes, until the filling is bubbling around the edges and the topping is golden. If the topping browns too quickly, loosely cover the dish with foil for the remaining bake time. Let the casserole rest for 5 to 10 minutes before serving so the sauce settles.
Tips
- Keep the vegetables dry: Drain them well after blanching. If using frozen broccoli or cauliflower, thaw and pat them dry; skip blanching if they are already tender, or they may become mushy.
- Shred cheese from a block: It usually melts more smoothly than pre-shredded cheese, which may contain anti-caking ingredients. Swiss varies in saltiness, so season the sauce gradually.
- Cut evenly: Similar-size pieces cook at a similar rate. Keep the vegetables bite-size and avoid packing them tightly into the dish, which can slow heating and leave the center cool.
- Make ahead carefully: Assemble the vegetable-and-sauce mixture up to one day ahead and refrigerate it covered. Add the breadcrumb topping just before baking; allow a chilled dish extra time in the oven and check that the center is hot.
Serving Suggestions
Serve this casserole warm as a hearty side with roast chicken, baked ham, pork chops, or a simple lentil loaf. It also pairs well with brown rice, mashed potatoes, or crusty bread to catch the cheese sauce. For a lighter plate, add a crisp green salad dressed with lemon or vinegar to balance the richness. The recipe makes about 6 side-dish servings, or 4 larger portions when served with a simple grain.
Variations
Use vegetables you have on hand, keeping the total amount close to 5 cups. Green beans, sliced mushrooms, zucchini, and corn all work; sauté mushrooms or zucchini first to cook off moisture. For a sharper flavor, replace up to half the Swiss with Gruyère or aged white cheddar. To make the topping gluten-free, use certified gluten-free breadcrumbs and replace the flour with an equal amount of a suitable gluten-free all-purpose blend. For extra crunch, mix 2 tablespoons finely chopped nuts into the breadcrumbs. If adding cooked chicken or white beans, use about 1½ cups and fold them in with the vegetables.
Storage and Reheating
Refrigerate leftovers in a shallow, covered container within 2 hours of baking. Keep them at 40°F (4°C) or below and use within 3 to 4 days. Reheat individual portions in the microwave until steaming hot throughout, stirring or turning midway where practical. To reheat a larger amount, cover the baking dish with foil and warm in a 350°F (175°C) oven until the center reaches 165°F (74°C), usually 20 to 30 minutes for a refrigerated portion; uncover for the last few minutes to refresh the topping. Avoid leaving the casserole at room temperature for more than 2 hours, or 1 hour when the temperature is above 90°F (32°C). Freezing is possible for up to 2 months, but the creamy sauce and vegetables may soften or separate after thawing; thaw overnight in the refrigerator and reheat thoroughly.
Frequently Asked Questions
Can I use frozen vegetables?
Yes. Thaw them completely and pat them dry before adding them. If they are already tender, there is no need to blanch them; simply fold them into the sauce and bake until the center is hot and bubbling.
Why is my casserole watery?
Vegetables can release water if they are not drained or dried well, and frozen vegetables often hold extra moisture. Blanch only until barely tender, drain thoroughly, and avoid adding vegetables straight from a package while still icy.
Can I make this casserole without blanching?
Blanching helps the carrots and sturdy florets soften evenly during the relatively short bake. You can instead steam the vegetables until just crisp-tender, then drain and dry them well. Raw carrots may remain too firm, so cut them very small if you choose not to precook them.
How can I tell when it is done?
The edges should bubble, the topping should be golden, and the center should be hot. If using a food thermometer, check the center; it should reach 165°F (74°C), especially if the casserole was assembled cold or includes cooked poultry.
Can I assemble it the night before?
Yes. Keep the assembled filling covered in the refrigerator and store the breadcrumb mixture separately. Add the topping before baking, and expect a chilled casserole to need extra time; use the bubbling edges and a 165°F (74°C) center as checks rather than relying on the usual bake time alone.