Combine crumbs and 4 tbsp. melted butter; set aside.
Add onion to remaining butter.
Sauté over low heat.
Add flour, salt and pepper.
Stir in cream and half and half in 1/8 cup increments.
Increase heat to medium; cook until bubbly and thickened, stirring constantly.
Add cheese; stir until smooth.
Stir in cooked carrots and parsley.
Spread in greased 9x13” baking dish.
Sprinkle with crumb mixture.
Cover casserole with foil.
Bake in 350° oven about 40 minutes.
Remove foil and bake an additional 5 minutes or until bubbly and crumbs are golden.