Potato-Tomato Gratin With Horseradish

Traditional cream-based potato gratins might be scandalized to know that this lighter olive-oil--based version dares to call itself a gratin as well. While it might not have the over-the-top indulgence of the original, this approach is still plenty rich and delicious. Tomatoes add intensity and jammy sweetness, brightened by the pungency of that winter underdog, fresh horseradish. The generous snow-like dusting of tangy grated horseradish on top adds a sinus-clearing peppery zing to the dish. The knobby cream-colored root looks similar to a parsnip, and you can find it in the refrigerated section of well-stocked supermarkets—though grated Parmesan would make a fine substitute. Serve the gratin as a side to a rich holiday meat like prime rib or simply on its own as a vegetarian main. —Christian Reynoso