Preheat oven to 350°. Spray an 8-inch square baking dish with cooking spray.

In a large Dutch oven, bring carrots and water to cover to a boil over medium-high heat. Cook until just tender, 6 to 8 minutes; drain well.

In a large skillet, melt butter over medium heat. Add onion and garlic; cook until softened, about 6 minutes.

Stir in flour; cook, stirring constantly, for 2 minutes.

Stir in milk; cook, stirring occasionally, until thickened.

Remove from heat, and stir in Cheddar, salt, and pepper until melted.

Stir in carrots until well combined. Pour mixture into prepared pan.

In a small bowl, stir together crackers, Parmesan, and melted butter; sprinkle onto casserole.

Bake until hot and bubbly, about 30 minutes.

Let stand for 10 minutes before serving.