2 1/4 to 2 1/2 pounds Swiss chard or rainbow chard (3 or 4 large bunches)
Kosher salt and pepper
4 tablespoons (1/2 stick) butter
1/4 cup flour
2 1/2 cups milk
Freshly ground nutmeg
One-third of Roasted Garlic Paste
2 cups shredded Parmigiano-Reggiano cheese
1 (24-inch) loaf French bread (3 inches wide)
If making this dish to serve on Cook Day, preheat the oven to 400°F. Otherwise, follow the make-ahead directions below.
Bring a large pot of water to a boil.
Stem the chard and keep the leaves whole. Salt the boiling water, wilt in the chard (the pot will be packed at first), then boil for 10 minutes. Place in a colander and run under cool water. Drain well and wring out excess liquids in a kitchen towel. Chop the leaves thoroughly.
Meanwhile, in a saucepan, melt the butter over medium heat. Whisk in the flour and cook 1 minute. Whisk in the milk and season with salt and pepper and a little nutmeg. Cook the sauce until thick enough to coat the back of a spoon. Stir in 1?3 cup of the garlic paste. Adjust the seasonings.
Layer half the greens in an 8 by 10-inch baking dish. Top with half the sauce and half the cheese. Repeat the layers, ending with cheese.
Make-ahead: Cool, cover, and refrigerate. Refrigerate the remaining garlic paste.
Night of: Return the casserole and garlic paste to room temp while you preheat the oven to 400°F.
Bake the chard 15 minutes. Remove from the oven and turn on the broiler.
Halve the loaf of bread crosswise, then split each piece horizontally to make a total of 4 (12-inch-long) pieces. Char the bread under the broiler for a minute, then slather with the garlic paste. Top each bread pizza with one-quarter of the chard au gratin. Cut each “pizza” in half and serve.