Fettuccine with Mushroom Alfredo

Ingredients

• 1 pound fettuccine
• 1 tablespoon olive oil
• ½ sweet onion, minced
• 2 garlic cloves, smashed
• 2 pints cremini mushrooms, thinly sliced, divided
• Salt and freshly ground black pepper
• 1 cup milk
• ½ cup finely grated Parmesan cheese