Summer Squash Gratin With Pickled Rye Bread Crumbs

Preparation

1. Step 1

   Heat the oven to 400 degrees. Slice squash ¼-inch thick, sprinkle with 2 teaspoons salt, and place in a colander set in the sink for at least 30 minutes and up to 1 hour, tossing occasionally with your hands. Gather the squash in a kitchen towel or paper towel and squeeze gently to remove excess moisture.

2. Step 2

   While the squash drains, melt 3 tablespoons butter in a 10-inch cast-iron skillet over medium heat. Add the breadcrumbs, 1 tablespoon pickle juice and ¾ teaspoon salt. Stir until all the butter is absorbed, transfer to a bowl and set aside. Wipe the skillet clean using a paper towel.

3. Step 3

   Heat 1 tablespoon butter in the skillet over medium-low. Add the onions and cook, tossing occasionally, until the onions are lightly caramelized, 15 to 20 minutes. Add the remaining 2 tablespoons pickle juice, the garlic, thyme, red-pepper flakes, pepper and ½ teaspoon salt and cook until the garlic is fragrant, about 1 minute. Off the heat, stir in 2 tablespoons butter until melted.

4. Step 4

   Add half the squash to the skillet and toss with tongs until combined. Add the rest of the squash and toss again. Add the Gruyère, along with ⅓ of the bread crumbs and toss well. Arrange into one packed layer, sprinkle with the remaining bread crumbs and bake until browned and bubbling, 30 to 35 minutes. Serve hot.