This creamy French onion broccoli cheese casserole has been a staple in my kitchen for years, and it shows up at casual weeknight dinners, holiday tables, and last-minute potlucks. I first combined these ingredients on a rainy evening when I wanted something warm, cheesy, and forgiving—something that would brighten the table without requiring a long ingredient list. The result was an irresistible mix of tender broccoli, rich creaminess from sour cream and condensed mushroom soup, and a bright savory note from the French onion soup mix. The crispy fried onions on top deliver that final crunchy contrast that keeps everyone coming back for seconds.

The texture is what makes this dish so memorable: soft, slightly roasted broccoli bites held in a custardy, savory sauce and blanketed with gooey cheddar. The French onion mix acts like a seasoning shortcut, bringing caramelized onion and beefy umami notes without hours of slow cooking. I love this casserole because it hits that comforting balance of creamy and crunchy, and it travels well—I've taken it to potlucks and family dinners where it never lasts long. If you appreciate easy, nostalgic food with a modern shortcut, this one will quickly become a favorite.

Ingredients

• Broccoli (4 cups florets): Use fresh florets if you can for the best texture; pick tight, bright-green crowns without yellowing. Frozen is an excellent, convenient option—just thaw and drain well to avoid excess water. Either yields tender florets that hold their shape after baking.
• Cream of mushroom soup (1 can, 10.5 oz): This condensed soup creates a silky sauce base. I recommend a brand you trust for flavor consistency; it adds umami and body. If you prefer homemade, reduce mushroom broth until thick and substitute one cup.
• French onion soup mix (1 packet): The packet brings savory, caramelized onion flavor without the time spent slowly cooking onions. It's the secret shortcut that lifts the whole dish. Look for a mix with quality onion flakes and minimal fillers.
• Sour cream (1 cup): Adds tang and creamy richness. Full-fat sour cream gives the most luxurious mouthfeel, but 2% works if you want to cut calories slightly. Stir gently to avoid curdling when combined with eggs.
• Eggs (2 large): Bind the mixture into a set, custardy texture. Room-temperature eggs incorporate more smoothly—take them out of the fridge 15 minutes before starting.
• Cheddar cheese (2 cups shredded): Sharp cheddar provides a bold cheesy flavor that stands up to the French onion seasoning. Shred from a block for better melt and flavor; pre-shredded often contains anti-caking agents and melts differently.
• Crispy fried onions (1 1/2 cups): The crunchy topping is essential—use the classic canned fried onions or homemade fried shallots for extra freshness. Add them at the end of baking to retain crispness.
• Salt (1/2 teaspoon) and Black pepper (1/4 teaspoon): Simple seasoning to balance flavors. Adjust to taste, especially if your soup mix or cheese is already salty.

Instructions

Preheat and prepare the dish: Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking dish well with butter or nonstick spray. Proper greasing prevents sticking and encourages even browning along the edges. If you prefer easier cleanup, line the dish with parchment leaving an overhang for lifting the casserole out. Blanch the fresh broccoli (or prepare frozen): If using fresh broccoli, bring a large pot of salted water to a boil and blanch the florets 2 to 3 minutes until bright green and just tender; immediately shock in an ice bath to stop cooking and preserve color, then drain thoroughly. For frozen broccoli, thaw completely and press out excess moisture in a clean kitchen towel or colander to avoid a watery casserole. Make the creamy mixture: In a large mixing bowl, whisk together the can of condensed cream of mushroom soup, 1 cup sour cream, 2 large eggs, the packet of French onion soup mix, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1 1/2 cups shredded cheddar. Whisk until smooth; the eggs will help set the filling while the sour cream and soup provide creaminess and flavor depth. If the mixture seems too thick, stir in a tablespoon of milk. Combine broccoli and sauce: Fold the drained broccoli into the sauce gently so the florets stay intact and evenly coated. Taste a small spoonful and adjust seasonings—add a pinch more salt or pepper if needed. The right balance here ensures each forkful carries both vegetable and savory sauce. Assemble and bake: Transfer the broccoli mixture to the prepared baking dish, spreading it into an even layer. Sprinkle the remaining 1/2 cup shredded cheddar evenly over the top. Bake uncovered for 30 to 35 minutes, until the casserole is heated through, bubbly around the edges, and the cheese has melted into the surface. Finish with crispy onions: Remove the casserole from the oven, sprinkle the 1 1/2 cups crispy fried onions over the top, and return to the oven for another 5 to 10 minutes until the onions are golden and crunchy. Let the dish rest for about 5 minutes before serving to allow it to set slightly for cleaner portions.

Storage Tips

To store leftovers, cool the casserole to room temperature, then cover tightly with plastic wrap or transfer into shallow airtight containers. Refrigerate for up to 3 to 4 days. For freezing, portion into individual foil containers or wrap the whole dish well with two layers of foil and a plastic bag; it will keep quality for up to 3 months. When reheating frozen portions, thaw in the refrigerator overnight and reheat in a 350°F oven until warmed through, about 20 to 30 minutes for single portions and 45 to 60 minutes for a full casserole, adding extra time as needed to restore the topping's crunch.

Ingredient Substitutions

If you need to adapt the dish, here are reliable swaps: for gluten-free, use a certified gluten-free condensed mushroom soup and gluten-free fried onions or toasted gluten-free breadcrumbs for the topping. To make it dairy-free, substitute vegan sour cream and dairy-free cheddar alternatives and use a mushroom-based dairy-free condensed soup—note the texture will be slightly less rich. For a lighter version, swap half-and-half for some of the sour cream and use reduced-fat cheese; you may want to reduce the baking time slightly to prevent over-browning.

Serving Suggestions

This casserole shines as a hearty side alongside roasted chicken, glazed ham, or grilled salmon. For a complete vegetarian meal, serve it with a crisp green salad dressed in a lemony vinaigrette and warm crusty bread. Garnish with chopped fresh chives or parsley for color and a hint of freshness. At holiday tables, pair it with roasted root vegetables and a bright cranberry relish to contrast the dish's creamy richness.

Seasonal Adaptations

In spring, add a handful of blanched asparagus tips or peas for a fresher profile. In autumn, mix in roasted butternut squash cubes for sweetness that plays well with sharp cheddar. For winter potlucks, consider adding a sprinkle of smoked paprika or a few teaspoons of Dijon mustard into the creamy base to introduce warmth and complexity that complements richer mains.

Meal Prep Tips

Assemble the casserole up to a day in advance, cover, and refrigerate. Bring it to room temperature for 20 minutes before baking and add 5 to 10 minutes to the bake time if baking straight from chilled. For individual lunches, divide into single-serving containers and freeze; reheat in the microwave and crisp the topping under a broiler for 1 to 2 minutes if desired. Use shallow containers to promote even reheating and faster cooling before refrigeration.

Success Stories

I’ve received messages from readers who made this for new homeowners, college potlucks, and family reunions—many noting how the French onion mix made the dish feel homemade and unique. One reader told me she doubled the recipe for a Sunday dinner and the leftovers were gone by Tuesday. Another family member described it as the perfect ‘weeknight comfort casserole’ that got picky eaters to try broccoli willingly for the first time.

Give this casserole a try and make it your own—swap cheeses, experiment with mix-ins, and don’t skimp on the fried onions if you love a crunchy finish. It’s reliable, comforting, and easy to adapt to whatever you have on hand.