Creamy Roasted Garlic Cauliflower Gratin

Ingredients

• 1 medium head garlic
• 3 tablespoons olive oil
• 1 large head cauliflower, cut into bite-size florets
• Kosher salt, to taste
• 2 tablespoons unsalted butter
• 2 tablespoons all-purpose flour
• 2 cups whole milk
• 1 tablespoon fresh thyme, finely chopped, plus more for garnish
• 4 ounces cream cheese, room temperature
• 3/4 cup sharp white cheddar, shredded, divided
• Freshly ground black pepper, to taste
• 1/4 cup parmesan cheese