Baked Pasta with Cauliflower and Swiss Chard
4 Tbsp unsalted butter, separated
2 Tbsp sliced garlic (from 3 to 4 cloves)
12 oz Swiss chard, stems sliced, leaves torn into 2-inch pieces
1 lb cauliflower, cut into small florets (4 cups)
1 Tbsp fresh sage leaves, chopped
Kosher salt and freshly ground pepper
1 lb pasta
2 Tbsp unbleached all-purpose flour
1 cup sour cream
8 oz Gruyère cheese, grated (2 cups) and separated
Preheat oven to 425°F. In a large, straight-sided skillet, melt half of butter over medium-high heat. Add garlic, chard stems, cauliflower, and sage; season with salt and pepper. Cook until garlic is golden, 2 minutes. Add 1/2 cup water; cover. Cook until cauliflower is just tender, 5 minutes. Transfer to a bowl; stir in chard leaves.
Cook pasta in a pot of salted boiling water until al dente. Drain, reserving 1½ cups water. Add remaining butter and flour to skillet; cook over medium-high heat, whisking, until toasted, 1 minute. Slowly whisk in pasta water until smooth. Bring to a boil; cook, whisking, until mixture coats the back of a spoon, about 2 minutes. Reduce heat to low; whisk in sour cream and 1½ cups cheese. Stir in pasta and chard mixture, pour into a lightly greased baking dish and top with remaining cheese. Transfer to oven; bake until cheese melts, about 10 minutes.