3 tablespoons unsalted butter
4 cups chopped red onion (about 4 medium)
2 tablespoons sugar
1 teaspoon fresh thyme leaves
3/4 teaspoon salt
1/2 teaspoon ground black pepper
2 bunches kale, about 16 ounces each, ribs removed and torn into 1 1/2-inch pieces
8 ounces Gruyere cheese, shredded
1/2 cup grated Parmesan cheese
2 1/2 cups heavy cream
- Melt 1 tablespoon of the butter in a large nonstick skillet over medium heat. Add the onion, sugar, thyme, 1/4 teaspoon of the salt and 1/4 teaspoon of the pepper; cook, stirring occasionally, until golden, about 18-20 minutes. Transfer to a bowl.
- Preheat the oven to 425°F.
- Wipe out the skillet and melt 1 tablespoon of the remaining butter over medium heat. Add half of the kale and cook, tossing, until slightly wilted, about 1 1/2 minutes. Transfer kale to the bowl with the onions; repeat with the remaining butter and kale.
- Add half of the Gruyere cheese, 1/4 cup of the Parmesan cheese, remaining 1/2 teaspoon salt and 1/4 teaspoon pepper to the kale mixture and toss well. Transfer to a nonstick 9 by 13-inch baking pan. Pour the cream over the kale then sprinkle with the remaining Gruyere and Parmesan cheeses.
- Bake in the center of the oven until the cream has thickened and the cheese is golden brown, about 53-55 minutes. Let stand 10 minutes before serving.