Saute onions on butter until tender. Stir in sour cream, dill, salt and half the cheddar. In separate bowl, combine corn, milk, cornbread mix, egg and hot sauce. Spray baking dish with non-stick cooking spray (I've used 10" square, 11x13, and a small oval pyrex - keep in mind that the smaller your dish, the thicker the "cake" will be, and will need to cook longer!) Put corn mixture in dish, and use a slotted spoon to spread onion mixture over corn mixture. Top with remaining cheddar and bake at 325-350 degrees for 30-40 minutes until top is crispy and brown and center is cooked through.