Preheat oven to 400°F. Grease or spray an 8- or 9-inch square baking dish (or other 2-quart baking dish) with nonstick cooking spray; set aside. Cook the broccoli in the microwave, just until crisp tender (about half of the time called for on the package). You don’t want to cook the broccoli until it’s too soft because it will continue cooking when you bake the casserole. Place the broccoli in colander to drain.
In a small saucepan over very low heat, stir together the condensed soup, cheese, and lemon juice, just until the cheese melts. Do not let the cheese get too warm, or it can separate resulting in a grainy texture.
In a separate bowl, whisk together the egg, mayonnaise, and grated onion. Combine the broccoli, soup mixture, and egg mixture. Transfer the mixture to the prepared baking dish.
In a small bowl, stir together the dry stuffing mix and the melted butter. Sprinkle the buttered crumbs on top of the casserole.
Bake for 15-20 minutes, or until heated through and topping is golden brown.
Video
Notes
Use fresh or frozen broccoli (about 9 cups fresh = two 10.8 ounce frozen bags).
Drain broccoli well to avoid watery texture.
If using frozen, cook only halfway before mixing.
For a lighter version, swap half the mayo for plain Greek yogurt.
For a no-soup version: whisk 2 tablespoons butter + 2 tablespoons flour, then add 1 cup milk and 1 cup shredded cheese until smooth. Taste and season with salt, pepper, and other herbs or spices.
Topping options: 3/4 cup stuffing mix, panko breadcrumbs, Corn Flakes crumbs, or crushed Ritz crackers + 2 tablespoons melted butter.
Store leftovers up to 3-4 days refrigerated or 3 months frozen.