When I travel, I bring a stack of food magazines to read for inspiration. On a particular cross-country flight, I was prepping for a new season of my TV show and saw a recipe for a parsnip gratin. I thought, “Well, parsnips are root vegetables. I love root vegetables in general. What if I just do a bunch of root vegetables all together in a gratin?” A few days later, I was basking in the creamy, cheesy glory of my latest creation. You’ll do the same. You can slice your root vegetables with a knife, but I recommend using my favorite kitchen utensil, the mandoline, and then taking care to spread the thin slices evenly. This dish transforms a quartet of ordinary roasted root vegetables that might not otherwise cohabit the same baking dish into old-fashioned, crowd-pleasing comfort food. Later, you can ask, “When was the last time anyone asked for more parsnips?”