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Creamy, cheesy, and flavorful, this easy vegetable casserole recipe is made with thawed frozen veggies for the easiest hearty veggie side dish with a surprisingly complex flavor. Only 5 ingredients and 5 minutes of prep time!
This vegetable casserole recipe is made with thawed frozen vegetables for the ultimate prep shortcut. As it bakes, the flavors meld and it tastes like it took hours! Plus, there’s a little salty crunch from the fried onions that will have your guests fighting over seconds.
Try this casserole instead of the usual green bean casserole at your next holiday feast or whip it up any day of the week for a hearty, flavorful easy side dish recipe. You really won’t believe how easy it is. This means more time for white cheddar mac and cheese, sweet potato casserole and scalloped potatoes! Or, if you are like me, that means time to make two more pie recipes!
Why you will love this dish:
- It requires only 5 ingredients and 5 minutes of prep time. I wasn’t kidding when I said this was an easy dish! You’ll be ready to pop this casserole in the oven after only 5 minutes of prep.
- This recipe easily scales up. It is easy to mix and bake a large batch of this easy vegetable casserole. Bake it in one large dish or divide it between multiple dishes. Just select the “2x” or “3x” buttons in the recipe card below to increase the number of portions.
- It’s a versatile side dish recipe. Serve it with Thanksgiving turkey, maple mashed sweet potatoes, and my easy dinner rolls! The creaminess of the dish also pairs beautifully with a simple side salad. Serve it with a roasted chicken or my foolproof rosemary chicken and this easy hashbrown casserole for an easy weeknight meal.
Professional Tips for Making Broccoli Cheese Casserole:
- It is easiest to place the bag of frozen vegetables in the refrigerator the night before to thaw, but I have also thawed them in the microwave at 50% power in a pinch.
- Be sure to drain any excess liquid from the vegetables before adding them to the casserole dish. Frozen vegetables can let off a good amount of moisture when defrosting or cooking, particularly if they have been in the freezer for a while.
- If you know you’ll have leftovers, only add fried onions to the section you are going to eat right away. Add the remaining onions to the dish when reheating so they keep their crunch.
- Mixed Frozen Vegetables: I use bags of frozen broccoli, carrots, and cauliflower in my vegetable casserole recipe, but you could certainly add other varieties. I used Trader Joe’s mixed veggies for this version. Every brand has a different size bag, so be sure to get enough.
- Sour Cream: I use full-fat sour cream but low-fat can also be used. Sour cream adds extra creaminess and tanginess to the Swiss cheese mixed vegetable casserole.
- Condensed Cream of Mushroom Soup: I use the organic Pacific brand cream of mushroom soup because I prefer the flavor and it has lower sodium than other brands, but you can use any brand you choose.
- Swiss Cheese: Swiss Cheese comes in a wide variety of qualities and flavors. You can use pre-shredded cheese, but I love to go the extra mile and shred my own. I look for Emmental cheese, which is a Swiss cheese from the Emmental region in Switzerland. It has a richer, more robust flavor than other varieties.
- Kosher Salt: Depending on the brand of soup you choose, you might need to add a little extra kosher salt to taste. Just like with my sweet potato casserole recipe with pecans, tasting along the way is the way to get the saltiness you desire!
- Black Pepper: A bit of freshly ground black pepper adds a nice kick to this recipe.
- French Fried Onions: French Fried Onions are a magical thing. Salty, crispy fried onions in a can! Add right before serving or they will get soggy.
See the recipe card for full information on ingredients and quantities.
- Ritz Crackers: If you aren’t a fan of fried onions, you can top the casserole with crushed Ritz crackers or any brand of butter crackers instead. It will provide the same crunch without the onion flavor.
- Different Cheese: You can try any variety of good melting cheese in this recipe. Cheddar cheese, mozzarella, Gruyère, and fontina are all great options.
- Corn Casserole: Feel free to add some frozen corn to this dish as well for added texture and flavor.
How to Make this Vegetable Casserole:
Use these instructions to make the perfect veggie casserole every time! Further details and measurements can be found in the recipe card below!
Step 1: Preheat your oven to 350°F.
Step 2: Combine the thawed vegetables, soup, ½ cup cheese, sour cream, and pepper. Pour into a 1-quart casserole dish.
Depending on the brand of soup you choose, you might need to add a little extra kosher salt to taste.
Step 3: Bake for 30 minutes covered.
Step 4: Top with remaining cheese and onions and bake uncovered for 5 minutes longer. Taste for seasoning, add salt if needed, and serve.
For the most impressive presentation, bring the whole casserole dish to the table so your guests can see the melty cheese lift out of the dish.
Chef Lindsey’s Recipe Tip
Frozen vegetables are a great way to increase your vegetable intake without the prep work of fresh vegetables. Frozen vegetables are typically flash-frozen at the peak of their nutrient density, allowing them to provide the same level of nutrition you would get from freshly picked vegetables!
Frequently Asked Questions
Refrigerate leftover vegetable casserole in an airtight container in the fridge for up to 7 days. Only add the fried onions when ready to serve the dish, as they will get soggy in the fridge. You can freeze this dish for up to 6 months. Transfer to a freezer-safe storage container or zip-top baggie after it has cooled and then place in the freezer.
To reheat from refrigerated, place in a covered, oven-safe dish in a preheated 350°F oven. Bake until hot and bubbly. Top with crispy onions and serve. To reheat from frozen, allow the casserole to thaw in the refrigerator overnight and follow the instructions above, or cover and bake from frozen in an oven-safe dish. It will take longer but will be equally delicious.
Because this recipe uses frozen, defrosted vegetables, they are already blanched, which means they are partially cooked. They will finish cooking while they are in the oven.
You can make this Swiss Cheese Mixed Vegetable Casserole up to 3 days ahead of serving. I recommend mixing the filling and then covering and refrigerating unbaked. It can also be baked ahead of time and rewarmed according to the instructions above.
If you tried this recipe and loved it please leave a 🌟 star rating and let me know how it goes in the comments below. I love hearing from you; your comments make my day!
- 16 oz frozen broccoli, carrots and cauliflower mix thawed and drained
- 12 oz condensed cream of mushroom soup canned I use organic Pacific brand but you can use a standard 10 oz can too
- 1 cup shredded Swiss cheese, divided 4 oz
- ⅓ cup sour cream
- ¼ teaspoon ground black pepper
- kosher salt to taste
- 2.8 oz French fried onions
- Preheat your oven to 350°F.
- Combine the thawed vegetables, soup, ½ cup cheese, sour cream, and pepper. Pour into a 1-quart casserole dish.
- Bake for 30 minutes covered.
- Top with remaining cheese and onions and bake uncovered for 5 minutes longer. Taste for seasoning, add salt if needed, and serve.
Before You Go!
I hope you enjoyed this professional chef-tested recipe. Check out our other delicious, chef-developed easy side dish recipes!