You can produce Cormeal with the Brickmill. Complete it and select the right ingredient.
After you have created the Brick Mill, you’ll need corn.
After you have harvested the corn, you can go to the Brick Mill and choose what you would like to grind and make.
After choosing the ingredient, you can then make, in this case, Cornmeal.
Here are some other ingredients you can make. Rye to get Rye Flour Grain to get Flour Corn to get Cornmeal.