Penne with Spinach and Ricotta

This is a good pasta dish,
the spinach and cheese go well together.
Sometimes I like to add some
red pepper flakes to spice it up a little.

Ingredients:
12 ounces penne pasta
2 tablespoons extra-virgin olive oil
4 scallions, thinly sliced
1 tablespoon chopped sage
Two 5-ounce bags baby spinach
2 tablespoons unsalted butter, cut into cubes
1 cup fresh ricotta cheese
1/4 cup freshly grated Parmigiano-Reggiano cheese, plus more for serving
Salt and freshly ground pepper

Directions:
In a large pot of boiling salted water,
cook the penne pasta until al dente.
Drain the pasta thoroughly,
reserving 1 cup of the pasta cooking water.
Meanwhile, in a large deep skillet,
heat the olive oil. Add the scallions and sage
and cook over high heat until lightly browned.
Add the spinach in large handfuls
and cook, stirring, until wilted.
Add the pasta, butter and ricotta and toss.
Add 3/4 cup of the reserved pasta
cooking water and the Parmigiano
and season generously with salt and pepper.
Cook over moderately low heat, tossing,
until the sauce is thick and creamy,
adding more of the pasta water as needed.
Transfer the paasta to bowls and serve right away,
with grated Parmigiano.