Preheat oven to 400 degrees F. Spray an 8- or 9-inch square baking dish with cooking spray and set aside.

Add potatoes to large pot of water and boil for about 10 minutes. When tender, drain and add to large bowl.

Meanwhile, cook broccoli in 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 soft because it will continue cooking when you bake the casserole. Place broccoli in colander to drain.

In a small saucepan over low heat, stir together condensed soup, cheese, and lemon juice, just until cheese melts.

In a separate bowl, whisk together egg, mayonnaise, and grated onion.

Add broccoli, soup mixture, and egg mixture to large bowl with potatoes. Stir to combine, coating broccoli and potatoes well. Transfer to prepared baking dish.

In a small bowl, stir together crushed crackers and melted butter. Sprinkle on top of the casserole.

Bake for 15-20 minutes, or until heated through and topping is golden brown.