1 tablespoon vegetable oil
1 onion, finely diced
2 cloves garlic, minced
1 tablespoon finely grated fresh ginger
1 teaspoon ground cumin
1 teaspoon garam masala
1/2 teaspoon turmeric
1/2 teaspoon salt
1 pinch cayenne pepper
8 cups chopped swiss chard, without stems (about 2 bunches, 10 stalks)
1/4 cup butter, melted
Kosher salt and freshly ground black pepper
In 8-inch nonstick ovenproof skillet, heat oil over medium heat. Cook onion, garlic and ginger together for about 8 minutes or until onion is softened. Add cumin, garam masala, turmeric, salt and cayenne pepper and stir until fragrant, about 1-2 minutes.
Add chard in big handfuls, stirring constantly and waiting until each batch is wilted before adding more (about 1 minute between each addition). Once all the chard has been added to the skillet, cook for about 3 minutes more, stirring occasionally. Transfer to a bowl. Do not clean the skillet.
Peel potatoes. Using mandoline or sharp knife, cut into paper-thin slices. Spread one-third of the potato slices on the bottom of the skillet you used to cook the chard and spices mixture, overlapping each slice a bit to create a pattern. Sprinkle potatoes with a pinch of kosher salt and freshly ground black pepper. Top with half of the chard mixture. Repeat layers once. Top with remaining potatoes, pressing well to evenly distribute. Pour melted butter over top.
Bake in 425F oven for about 50 minutes or until potatoes are tender when pierced with a knife. Let rest for 10 minutes before serving, or let cool to room temperature and serve that way.