Green Bean Casserole

1 1/2 Tbsp butter
3 Tbsp all-purpose flour
1 1/2 C milk
2-4 tsp dry ranch-style salad dressing mix
1/4-1/2 tsp white pepper
1 C chopped onion
2 cloves garlic, minced
1 1/2 C sliced fresh mushrooms
1 1/4 pounds fresh green beans, cooked until crisp-tender
1 C fresh bread crumbs, toasted

Melt butter in small saucepan over low heat. Stir in flour; cook 1-2 minutes stirring constantly. Using wire whisk, stir in milk; bring to a boil. Cook, whisking constantly, 1-2 minutes or until thickened. Stir in dressing mix and white pepper; set aside. Preheat oven to 350. Spray medium skillet with nonstick cooking spray; heat over medium-high heat. Add onion and garlic; cook and stir 2-3 minutes or until tender. Remove half of onion mixture; set aside. Add mushrooms to onion mixture in skillet and cook 5 minutes or until mushrooms are tender. Combine mushroom mixture, green beans and white sauce in 1 1/2 quart casserole. Combine bread crumbs with reserved onion mixture; sprinkle over casserole. Bake, uncovered, until heated through, about 20-30 minutes.