Cheddar Cauliflower and Roasted Garlic Soup (Creamy and Cozy)

Ingredients

• 2 large heads cauliflower, cut into florets, about 2 1/2 lb (1.1 kg)
• 1 whole garlic bulb
• 2 tablespoons olive oil, divided
• 1 teaspoon kosher salt, divided
• 1/2 teaspoon black pepper, divided
• 2 tablespoons unsalted butter
• 1 medium yellow onion, diced
• 1 medium carrot, diced
• 2 celery ribs, diced
• 1 teaspoon dried thyme
• 4 cups (950 ml) vegetable broth
• 1 cup (240 ml) whole milk
• 1/2 cup (120 ml) heavy cream
• 2 cups (225 g) freshly shredded sharp cheddar cheese
• 2 tablespoons chopped fresh chives, for serving