Preheat oven to 350 degrees F. Spray a 13 x 9 inch baking dish with nonstick cooking spray.
Remove leaves and bottom, tough stem of cauliflower, leaving the rest of the head whole. Cover with water in a deep saucepan, and boil, covered, until knife tender but not mushy.
Cut cauliflower into florets.
Meanwhile, melt 1 stick butter and sour cream in a small saucepan; stir until smooth.
In a small skillet, melt 1 stick butter, add crushed butter crackers and brown lightly.
Add cauliflower to prepared baking dish; sprinkle buttered cracker crumbles over top. Pour sour cream sauce slowly over top.
Bake for approximately 30 to 40 minutes or until hot and bubbly.
The the casserole sit on the counter for 5 to 10 minutes to set up before serving, if desired.