To prepare a vegetarian creamed corn casserole from scratch, you'll first need to prepare the corn. Peel and slice the kernels off the ears of corn and cut them into small cubes. Add the cubed corn to the bowl of ice water and stir to combine. Pour the mixture into the bottom of the casserole dish and bake in the oven at 350 degrees F for 45 to 50 minutes, or until the top is brown and bubbly. Serve with sour cream and shredded cheddar cheese.