This creamy French onion broccoli cheese casserole is one of those dishes I turn to when I want comfort food that feels indulgent but still feeds a crowd. I first made this on a chilly autumn evening when I had a bag of frozen broccoli and a few pantry staples on hand. The combination of tangy sour cream, savory French onion seasoning, and melty cheddar created a sauce that clung to every floret, while the crispy fried onions on top added that irresistible crunch. It quickly became the side dish everyone asked for at family dinners and potlucks.

I love how forgiving this recipe is: it works with fresh or frozen broccoli, you can use a can of condensed soup from your pantry, and it finishes in the oven in under an hour. The texture is creamy without being soupy, and the flavor balance — savory mushroom-and-onion base with bright broccoli and sharp cheddar — is what keeps people going back for seconds. Serve it alongside roasted chicken or let it stand on its own for a meatless weeknight supper. The dish also reheats beautifully, which makes it perfect for leftovers or make-ahead entertaining.

Ingredients

• Broccoli (4 cups): Use fresh florets trimmed into small, bite-size pieces if possible; if using frozen, choose one labeled "cut florets" and thaw completely before draining. Fresh will give slightly firmer texture, frozen is convenient and yields a creamier final dish.
• Cream of mushroom soup (1 can, 10.5 oz): This provides a savory, velvety base. Campbell’s or store-brand condensed mushroom soup both work well; if you prefer a lower-sodium option, look for reduced-salt varieties but check seasoning before baking.
• French onion soup mix (1 packet): The seasoning packet (e.g., Lipton) adds concentrated onion flavor and savory depth — it’s a signature element here and wakes up the broccoli and cheese.
• Sour cream (1 cup): Full-fat sour cream gives the best texture and tang; nonfat or lighter versions can be used, but the casserole will be less rich and slightly looser when baked.
• Large eggs (2): Eggs act as a binder and help set the filling into a creamy custard when baked. Use room-temperature eggs to help the filling heat evenly.
• Shredded cheddar cheese (2 cups): Sharp cheddar offers the best flavor contrast to the sour cream and French onion seasonings. Buy a block and shred it yourself for better melt and flavor compared to pre-shredded cheeses that contain anti-caking agents.
• Crispy fried onions (1 1/2 cups): These are the finishing touch — store-bought French-fried onions add crunch and a toasted onion flavor. Reserve a small amount to add after baking for extra texture if desired.
• Salt and black pepper: 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper — taste your assembled mixture before baking and adjust if using low-sodium soup or pre-salted crispy onions.

Instructions

Preheat and prepare the dish: Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish with butter or nonstick spray. Preheating ensures the casserole begins baking immediately for even set and a golden top. A glass or ceramic pan works well, but reduce oven temp by 25°F if using a dark metal pan to prevent over-browning. Blanch or prepare the broccoli: If using fresh broccoli, bring a pot of salted water to a boil and blanch florets for 2–3 minutes until bright green and just tender. Immediately transfer to an ice bath to stop cooking and preserve color, then drain thoroughly. If using frozen broccoli, thaw completely and press out excess water using a clean towel or colander to avoid a watery casserole. Mix the creamy base: In a large bowl, whisk together the 10.5-ounce can of cream of mushroom soup, 1 cup sour cream, 2 large eggs, 1 packet French onion soup mix, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1 1/2 cups of shredded cheddar. Mixing thoroughly ensures the eggs are evenly distributed and the seasoning dissolves into the sauce for consistent flavor. Combine with broccoli: Gently fold the prepared broccoli into the creamy mixture until each floret is well coated. Over-mixing can break the florets, so use a folding motion to preserve shape. Taste a small amount of the mixture and adjust salt or pepper if needed before transferring to the baking dish. Assemble and top: Spread the broccoli mixture evenly into the prepared 9×13-inch dish. Sprinkle the remaining 1/2 cup of cheddar cheese evenly over the top for a melty, browned layer. Leaving it uncovered allows the cheese to bubble and the top to set. Bake and finish: Bake uncovered at 350°F for 30–35 minutes until the casserole is hot, bubbling at the edges, and the center registers about 165°F on an instant-read thermometer. Remove from the oven, sprinkle the 1 1/2 cups of crispy fried onions across the surface, and return to the oven for another 5–10 minutes until the onions are golden brown. Let rest 5 minutes before serving to allow the custard to set.

Storage Tips

Store leftovers in an airtight container in the refrigerator for up to 3–4 days. To reheat, place individual portions in a microwave-safe dish and heat for 1–2 minutes, or warm the entire casserole in a 350°F oven for 15–20 minutes until heated through. If frozen, thaw overnight in the refrigerator before reheating where possible. Keep the fried onions separate and add them right before serving to preserve crunch.

Ingredient Substitutions

Want to modify the casserole? Swap the cream of mushroom soup for cream of chicken or a homemade white sauce (béchamel) if you prefer fewer preservatives. Replace sour cream with Greek yogurt for a tangy but slightly less rich result, using a 1:1 ratio. For a gluten-free version, use gluten-free condensed soup and gluten-free fried onions or substitute crushed gluten-free crackers for the topping. Try smoked cheddar or Gruyère instead of sharp cheddar for a deeper, nuttier flavor.

Serving Suggestions

Serve this alongside roast chicken, glazed ham, or as a vegetarian main with a crisp green salad. Garnish with chopped fresh chives or parsley for color and freshness. For holiday tables, pair it with roasted root vegetables and crusty bread. Leftovers also make a satisfying filling for baked potatoes or as a warm topping for quinoa bowls.

Cultural Background

This casserole blends American comfort-cooking traditions — condensed soup-based casseroles and convenience toppings like French-fried onions — with classic French onion flavors. While not a traditional French dish, the use of French onion seasoning evokes the caramelized onion profiles found in French onion soup, reimagined here in a creamy, vegetable-forward side that echoes mid-20th-century casserole culture.

Seasonal Adaptations

In spring and summer, use fresh broccoli for a brighter texture and fold in a handful of blanched asparagus tips. In fall and winter, add roasted mushrooms or caramelized onions for deeper umami. For a holiday twist, stir in 1/2 cup cooked pancetta or diced ham for extra savory richness, and top with a mix of panko and grated Parmesan instead of fried onions for a golden crust.

Meal Prep Tips

For batch cooking, prepare and assemble the casserole in the baking dish up to 24 hours in advance; cover tightly and refrigerate. When ready to serve, bake directly from the fridge for an additional 5–10 minutes on top of the recommended time. If you plan to freeze, assemble without the fried onions, wrap tightly with plastic and foil, and bake from frozen — add the topping during the final 10 minutes for best texture.

This casserole is a comforting, versatile dish that invites experimentation and makes weekday dinners easier. It’s both familiar and a little bit special — a dependable recipe that brings smiles at the dinner table. Try it once and you’ll understand why it stays in my regular rotation.