Best Mashed Potato Casserole Recipe - How To Make Mashed Potato Casserole

Ingredients

• 1 c. whole milk
• 6 sprigs thyme
• 2 dried bay leaves
• 6 tbsp. (3/4 stick) unsalted butter, divided, plus more for pan
• Kosher salt
• Freshly ground black pepper
• 4 lb. Yukon gold potatoes, peeled and cut into 1" pieces
• 3 cloves garlic, smashed and peeled
• 8 oz. cream cheese, room temperature
• 1/2 c. finely grated Parmesan (about 2 oz.), divided
• 2 large eggs, beaten to blend
• 1 c. panko bread crumbs
• Sliced chives, for serving