Preheat your oven to 350°F (175°C) and prepare your baking dish with butter.

Prepare the carrots by peeling, dicing or shredding, and steaming or boiling until tender.

In a medium saucepan, melt butter, whisk in flour, and gradually add milk, stirring until smooth. Add cheddar cheese and stir until melted.

Combine the carrots with the cheese sauce in a mixing bowl and transfer to the baking dish.

In a small bowl, mix crushed cornflakes with melted butter, then sprinkle over the casserole.

Bake in the oven for 25-30 minutes until golden brown and bubbly.

Allow the casserole to cool for 5-10 minutes before serving.