Preheat Oven to 350F.
Combine crushed corn flakes and all the melted butter in a small bowl. Set aside.
In a pot over medium-high heat bring water to a boil. Add in your onions, carrots, salt and pepper. Turn down to a low simmer and parboil ingredients until tender. Strain if necessary.
In another pot melt 1 tbsp of butter over med-high heat. Add your flour stirring for 1 - 2 minutes. Slowly pour in your milk until all combined. Let mixture thicken. Whisk in cheese a handful at a time.
Oil or butter your casserole dish. Add carrot mixture and stir in your cheese sauce. Top with crushed corn flake/butter and bake for 20-25 minutes. Take out of oven and allow to cool a few minutes before serving.