How to Make It
Boil pasta and kale together in a large pot of boiling salted water until the pasta is al dente and the kale is tender. Drain the pasta and kale in a colander.
While the pasta and kale are cooking, in a medium saucepan, heat the butter over medium high heat until hot. Whisk in the flour and cook, stirring, 2 minutes. Whisk in the milk in a steady stream and bring to a boil, whisking. Boil the milk sauce until slightly thickened, about 5 minutes. Stir in half the feta and 1/2 teaspoon each salt and pepper. Toss the sauce with the pasta and kale, then season to taste with salt and pepper. Sprinkle the remaining feta over the pasta and serve.