Meatloaf with Stroganoff Sauce

Ingredients

• 1 1/2 lb. ground beef
• 3/4 c. quick oats
• 1 c. milk
• 1 egg
• 1 t. Worcestershire sauce
• 1/2 t. kosher salt
• 1/2 t. black pepper
• 1/2 t. sage
• 1/2 t. celery salt
• 1/2 t. garlic powder
• 1/2 t. onion powder
• 2 T. butter
• 1 small onion, thinly sliced (about 3/4 c.)
• 2 large garlic cloves, minced
• 8 oz. crimini or white button mushrooms, sliced
• 1 c. beef broth
• 2 T. all-purpose flour
• 1/2 c. sour cream
• 1/2 t. freshly ground black pepper
• chopped parsley, for garnish