Cheesy Chicken Penne Bake

Ingredients

• 1 lb boneless, skinless chicken breast, diced into bite-sized pieces
• 1 tablespoon olive oil
• 1 cup whole milk
• 1/4 teaspoon salt
• 2 cups dry penne pasta
• 1/4 teaspoon pepper
• 1 1/2 cups grated cheddar cheese, divided
• 1 cup sliced fresh mushrooms
• 1 tablespoon all-purpose flour
• 1/4 cup sour cream
• 1 tablespoon butter
• 1/2 cup diced onion