01 - Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
02 - In a large skillet, melt 2 tablespoons butter over medium heat. Sauté the chopped onion for 3 to 4 minutes until translucent. Add minced garlic and cook for 1 minute longer.
03 - In a large mixing bowl, combine broccoli florets, sautéed onion and garlic, condensed soup, sour cream, milk, beaten eggs, Dijon mustard, salt, and pepper. Fold in 1 1/2 cups of shredded cheddar cheese until evenly incorporated.
04 - Transfer the broccoli mixture into the prepared baking dish and spread evenly. Sprinkle the remaining 1/2 cup of cheddar cheese over the top.
05 - In a small bowl, stir together the crushed crackers and olive oil or melted butter. Distribute the mixture evenly over the casserole.
06 - Bake for 30 minutes, or until the casserole is bubbling and the topping is golden brown. Allow to rest for 5 minutes before serving.