Slowly melt 2 Tablespoons butter and the cheese in a saucepan over low heat with the milk, and whisk in the arrowroot to get it all creamy. Pour the cheese sauce over the broccoli.
Then for the topping melt the 1/2 cup butter and stir in the crackers. Sprinkle over the top of the broccoli and cheese sauce. Bake 20 minutes at 350* or until hot all the way through