Preheat your oven to 350°F (175°C). Spray an 8-inch square baking dish with cooking spray.

In a large Dutch oven, bring enough water to cover the carrots to a boil. Add the carrots and cook for about 6 to 8 minutes until tender. Drain and set aside.

In a skillet, melt butter over medium heat, add onion and garlic. Sauté for about 6 minutes until softened and fragrant.

Stir in flour to the onion and garlic mixture for about 2 minutes, then gradually add milk, stirring until thickened (3 to 5 minutes). Remove from heat and stir in cheddar cheese, salt, and pepper until melted.

Gently fold boiled carrots into the cheese mixture until coated. Pour the mixture into the baking dish and spread evenly.

In a bowl, combine crushed crackers, Parmesan cheese, and melted butter. Sprinkle the mixture evenly over the casserole.

Bake in the oven for about 30 minutes until bubbling and golden brown on top.

Let the casserole sit for about 10 minutes before serving.