Chef Sarah Heller takes advantage of the heartier greens of spring—Swiss chard and leafy beet greens—for this creamy baked side dish, though sturdy greens like kale or spinach would also work here. She then adds hazelnuts for crunch and bakes the gratin until bubbly and golden. Slideshow: More Swiss Chard Recipes
How to Make It
Preheat oven to 350°F. Coat an 8-inch square baking dish with oil.
Prepare a large bowl of ice water. Bring a large pot of water to a boil over high. Add greens, return to a boil, and cook until tender, about 2 minutes. Drain greens, and plunge immediately into ice water. Once cool, drain well, and squeeze out excess water. Roughly chop greens. Set aside.
Melt butter in a large, deep skillet over medium. Add onion, and cook, stirring occasionally, until translucent, about 6 minutes. Sprinkle flour over onions, stir until evenly coated, and cook 1 minute. Whisk in milk, and simmer 2 minutes. Stir in 1/4 cup Parmesan, salt, orange zest, and pepper. Stir in chopped greens.
Pour mixture into prepared baking dish; top evenly with hazelnuts and remaining 1/4 cup Parmesan. Bake in preheated oven until golden brown and bubbling, 30 to 40 minutes.