INSTRUCTIONS

1. Arrange rack in center of oven. Preheat to 375°F. Generously butter a 9x13-inch baking dish and set aside.
2. Boil a large pot of salted water. Slice chard leaves roughly into 2-inch pieces (you should have about 10 cups). Add chard to boiling water and cook until bright green and tender, about 1 minute. Using a spider, transfer to a large bowl of ice-cold water. Once cool, drain well. Place chard into a clean tea towel. Wring out chard to extract excess liquid. Transfer to a small bowl or plate, breaking up with your fingertips to separate leaves, and set aside.
3. Return water to a boil, then add pasta. Cook, stirring occasionally, until soft but slightly undercooked (pasta will continue cooking in sauce), about 8 minutes. Drain well and let it cool while preparing sauce.
4. Toss 1 cup fontina with gruyere and cheddar cheese in a medium bowl to combine. Set aside.
5. Return the same large pot to medium heat, then add butter. Once melted, add flour and cook, whisking constantly, for 2 minutes. Whisk in milk and continue cooking until the sauce is thick enough to lightly coat the back of a spoon, about 8 to 10 minutes (mixture will be thin). Remove from heat, then whisk in half of cheese-mixture, one small handful at a time, just until melted and combined. Whisk in mustard and salt. Season with fresh pepper. Stir in the pasta until fully incorporated using a spatula. Stir in Swiss chard, ensuring leaves are fully distributed. Sprinkle in remaining cheese-mixture, stirring quickly just to combine. Scrape into prepared pan. Sprinkle over remaining ½ cup fontina.
6. Bake in center of oven until golden-brown, approximately 25 to 30 minutes. Let it stand for 15 minutes before serving.