Melt butter in medium saucepan. Add garlic and cook gently until soft. Whisk in flour and cook until faintly nutty in aroma. Add milk gradually, allowing mixture to thicken after each addition. When all milk is added, season and remove from heat.
Stir in all other ingredients.
Pour into a buttered baking dish and sprinkle with breadcrumbs and additional cheddar. Bake at 375 until bubbly and golden, about 30 to 40 minutes.