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Six layers of colorful vegetables cook together in this free-form gratin; panko and Parmigiano-Reggiano absorb extra juices and provide a nice crunch. Dial in your knife skills or use a mandoline to cut the vegetables into thin, uniform slices to ensure easy layering and even baking. To make serving easy, allow the gratin to cool for 20 minutes before cutting.

Justin Chapple
Justin Chapple
June 2021

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Read the full recipe after the video.

Recipe Summary

active:
45 mins
total:
2 hrs 25 mins
Servings:
8
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Ingredients

Ingredient Checklist

Directions

Instructions Checklist
  • Preheat oven to 350°F with rack in middle position. Line an 18- x 13-inch rimmed baking sheet with parchment paper or aluminum foil; grease with oil. Stir together panko, cheese, thyme, 1 teaspoon salt, and 1/2 teaspoon pepper in a small bowl; set aside.  

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  • Trim and remove stem end and outer layer of onion, and discard. Using a sharp knife or a mandoline, slice onion into wafer-thin slices (about 1/16 inch thick). Set aside.  

  • Arrange Yukon gold potato slices in lengthwise rows to create a roughly 13- x 9-inch rectangle on prepared baking sheet, overlapping slices slightly. Sprinkle evenly with 1/4 teaspoon salt, 1 pinch of pepper, and 1/4 cup loosely packed panko mixture. Repeat layering process with onion, sweet potato, zucchini, and yellow squash slices, overlapping slightly and sprinkling with 1/4 teaspoon salt, 1 pinch of pepper, and 1/4 cup loosely packed panko mixture between layers. Top with tomato slices, overlapping slightly. Gently press down to even out layers. Sprinkle evenly with remaining 1/4 teaspoon salt. Top with a piece of parchment paper; cover sheet pan tightly with foil. Bake in preheated oven until a paring knife inserted in gratin meets only slight resistance, about 1 hour.  

  • Remove from oven; remove and discard foil. Sprinkle gratin evenly with remaining 1/2 cup panko mixture. Rotate pan from front to back, and return to oven on middle rack. Bake, uncovered, at 350°F until a knife inserted in gratin goes in and comes out easily, about 20 minutes. Increase heat to broil. (Do not remove gratin from oven.) Broil until panko is lightly browned, 2 to 3 minutes. Remove from oven; let cool 20 minutes.

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