Velvety Winter Squash Soup with Smoky Garlic Custard

Name: Velvety Winter Squash Soup with Smoky Garlic Custard
Ingredients: 4 pounds winter squash, such as butternut, halved lengthwise, seeds and fibrous material removed; 2 heads garlic; 1 tablespoon extra-virgin olive oil; 2 tablespoons unsalted butter; 3 large leeks, trimmed, sliced lengthwise and rinsed well, white part only finely chopped; 5 cups unsalted chicken or vegetable broth, plus more as needed; 1 ¾ teaspoons smoked salt, divided (see Note); ½ teaspoon ground white pepper, divided; 2 cups whole milk; 7 large egg yolks; Finely grated Parmesan cheese and snipped fresh chives for garnish