Best Green Bean Casserole - VeryVera

Ingredients

• 2 lb green beans
• Kosher salt
• 2 tbsp. olive oil, divided
• 1 lb cremini mushrooms, sliced, divided
• 6 tbsp. unsalted butter, divided
• 4 large sprigs thyme
• 2 tbsp. all-purpose flour
• 1 ¼ cups whole milk
• 1 c heavy cream
• 4 garlic cloves, finely grated
• ½ cup grated Parmesan
• Freshly ground black pepper
• ¾ cup French’s fried onions