Celery Root Purée with Toasted Hazelnuts

Name: Celery Root Purée with Toasted Hazelnuts
Ingredients: 3 pounds celery root, peeled, cut into ½” cubes; 3 pounds russet potatoes, peeled, cut into 1” cubes; Kosher salt; ⅔ cup heavy cream; ⅔ cup whole milk; ½ cup (1 stick) chilled unsalted butter, cut into ½” cubes; Freshly ground black pepper; 1 tablespoon good-quality hazelnut oil; ¼ cup coarsely chopped toasted hazelnuts