Preheat oven to 350°F (175°C).

Cook broccoli until slightly tender but still firm.

Drain broccoli thoroughly.

In a greased casserole dish, mix the beaten egg, cream of mushroom soup, mayonnaise, grated onion, lemon juice, and grated Cheddar cheese.

Layer half of the cooked broccoli in the casserole dish.

Pour half of the cream of mushroom mixture over the broccoli.

Repeat the layers with the remaining broccoli and cream of mushroom mixture.

Crush Ritz crackers and sprinkle over the top of the casserole.

Dot the top with butter.

Bake in the preheated oven for 30 minutes, or until golden brown and bubbly.