The Best Root Vegetable Gratin

Name: The Best Root Vegetable Gratin
Ingredients: ¼ cup white miso paste (not low-sodium); 1 ½ cups heavy cream or rich cashew milk; 1 ½ cups vegetable or chicken broth; 6 garlic cloves (minced); 2 Tablespoons fresh thyme leaves (or 2 teaspoons dried thyme); 1 teaspoon black pepper; A big pinch of salt; ¼ teaspoon ground nutmeg; ¼ cup caramelized onion jam (I used Divina or saute 1 onion, diced); 4 pounds mixed root vegetables; 1-2 cups shredded Gruyere or Comte cheese; Olive oil; Salt to taste