3 tablespoons unsalted butter

1/4 cup all-purpose flour

3 cups whole milk

1 cup finely grated Parmesan cheese (about 4 ounces)

Coarse salt and freshly ground pepper

4 cups coarsely chopped Swiss chard (about 1 bunch)

3/4 pound sweet Italian sausage, casings removed

1 lemon, very thinly sliced

6 no-boil lasagna noodles, preferably Barilla