Ingredients:
6 tablespoonsolive oil, divided
1 large Vidalia or yellow onion, thinly sliced
1 large sweet potato (¾ to 1 pound), chopped into ¾-inch pieces
2 garlic cloves, thinly sliced or finely chopped
1/4 teaspoonred pepper flakes, or to taste
Kosher salt and freshly ground pepper
2 tablespoonstomato paste
3 cupschopped kale (Tuscan or curly; from about ½ medium bunch)
1 1/2 cupsFrench lentils
1 (14.5-ounce) can diced tomatoes, plus juices
3 1/2 cupswater
1 tablespoonDijon mustard
1 cuppanko breadcrumbs
1 (4- to 5-ounce) log chèvre (fresh goat cheese), plain or herbed, crumbled
Directions:
Heat the oven to 400°F. In a 12-inch ovenproof sauté pan or skillet with 2-inch sides (or a 3 1/2-quart braising pan), heat 4 tablespoons of the oil over medium heat. Add the onion and cook, stirring occasionally, for 3 to 4 minutes, until starting to soften. Add the sweet potatoes, garlic, red pepper flakes, and a pinch of salt and pepper. Cook, stirring occasionally, for another 3 to 4 minutes, until the outsides of the sweet potatoes start to lose their firmness.
Add the tomato paste and continue to cook, stirring constantly and reducing the heat as needed to avoid burning, for 2 to 3 minutes, until it caramelizes and changes in color from bright to brick red.
Add the kale, lentils, diced tomatoes (plus their juices), water, and 1¾ teaspoons of salt. Bring to a boil, then reduce the heat to medium-low and maintain a rapid simmer for 3 minutes.
Transfer the pan to the oven. Bake for 20 minutes. Stir the lentils and pat them back down in the pan. Continue to bake for about 15 minutes more, until the lentils are tender and most of the liquid has evaporated.
Meanwhile, prepare the crumb topping: In a medium bowl, stir the mustard and the remaining 2 tablespoons of the oil. Add the panko, ¼ cup at a time, tossing and stirring until the crumbs are coated in the mustard and oil. Mix in the chèvre; season with a few pinches of salt and pepper. Scatter the topping evenly across the top of the lentils.
Heat the broiler (to medium if your broiler has different settings) with the oven rack about 8 inches from the heating element. Broil, checking often and rotating the pan a few times, for 2 to 4 minutes, until browned and crunchy. (Tip: Lightly rake or stir the crumbs a few times to ensure they get evenly browned and crunchy.) Alternatively, bake the gratin for 10 to 15 minutes more, until the topping is golden brown. Serve warm.