Serves: 4 | Prep time: 15 minutes | Cook time: 35 minutes

Ingredients

3 tablespoons butter, divided, plus more for the bread
2 cooking onions, thinly sliced
1/2 teaspoon kosher salt
3 cups kale, stems removed and leaves chopped
8 slices sourdough bread
1 tablespoon dijon mustard
2 cups grated sharp cheddar or gruyere
1 apple, cored and thinly sliced

Directions

• Melt 2 tablespoons of the butter in a large skillet over medium-low heat. Add the onions and salt and cook for 20 to 25 minutes, stirring now and then, until deep golden and jammy.
• Add the kale and the remaining 1 tablespoon of butter and cook for 2 to 3 minutes, until wilted. Transfer to a bowl and wipe out the skillet.
• Butter one side of each bread slice. Flip 4 slices over and spread the plain sides with dijon.
• Layer half of the cheese on the dijon, then the onion and kale mixture, the apple slices, and the remaining cheese. Top with the remaining bread, buttered side out.
• Cook in the skillet over medium-low heat for 3 to 4 minutes per side, covered, until the bread is golden and the cheese is melted.