Preheat your oven to 350°F (175°C).
Grease a 9x13-inch baking dish.
Steam the broccoli florets until slightly tender (about 3-5 minutes).
In a large bowl, mix the sour cream, mayonnaise, and chopped onion.
Add the steamed broccoli to the mixture and stir well.
Fold in half of the shredded cheddar cheese.
Transfer the mixture to the prepared baking dish.
In a separate bowl, combine crushed crackers and melted butter.
Sprinkle the cracker mixture evenly over the broccoli.
Top with the remaining cheddar cheese.
Bake for 30 minutes until bubbly and golden brown.