This gorgeous gratin is layered with flavor. It’s impressive—and delicious—served beside a main dish, but is strong enough on its own to claim center stage.
Heat 2 tablespoons red palm oil in a large sauté pan over medium heat. Sauté the onions and rosemary for 15-20 minutes, turning with a stiff spatula occasionally in the beginning, and frequently near the end. Season with salt and pepper and remove to a bowl.
Add the Swiss chard to the pan and toss to coat with any oil remaining. Cook for 4-5 minutes, until wilted. Add garlic to the chard with a pinch of salt and pepper and toss to coat. Cook another 3-4 minutes, until chard is thoroughly wilted and liquid has evaporated. Add chard to the onions and toss well to mix.
Preheat oven to 400.
Heat remaining 1 tablespoon red palm oil in a medium saucepan over medium heat. Add shallot and sage and sauté for 3 minutes, until fragrant. Add flour and chipotle powder and pour in milk, whisking until smooth. Bring mixture up to a gentle boil, whisking frequently, for 5-7 minutes, until thick and smooth. Season with salt and pepper.
Rub the bottom of 13×9 glass dish with the halved clove of garlic. Spiral half of the potatoes evenly on the bottom of the pan. Top with half the onion and Swiss chard mixture, half the sauce and half the cheese. Repeat with another layer.
Cover and bake for 40 minutes. Uncover and bake another 30 minutes, until the potatoes are tender and the cheese and sauce are golden on top.