This rustic pasta sauce consists of mainly one ingredient: broccoli. The broccoli is boiled until very tender and then mashed with a fork. Simply toss the mashed broccoli with pasta water and some cheese to make a delicious and nutritious sauce.
Bring a large pot of salted water to a boil. Add the broccoli and cook until very tender, 7 to 8 minutes. Remove the broccoli to a paper towel–lined plate using a slotted spoon, reserving the water in the pot. Add the pasta to the boiling water, stir and cook as the label directs for al dente. Reserve 1 cup cooking water, then drain.
Meanwhile, pat the broccoli dry and transfer to a bowl. Using a fork or potato masher, mash the broccoli until mostly smooth but still slightly chunky.
Heat the olive oil in a large skillet over medium heat. Add the garlic and red pepper flakes and cook until starting to sizzle and the garlic is just browning, 1 to 2 minutes. Add the broccoli and combine with a rubber spatula, lightly mashing it with the oil and cooking down the broccoli a bit further, 2 to 3 minutes.
Add the pasta and 1/2 cup of the reserved cooking water to the skillet. Stir to combine and add the cheese. Continue to fold the broccoli and pasta together until the sauce coats the pasta, adding more cooking water as needed to loosen, 2 to 3 minutes. Season with salt and pepper. Turn off the heat and stir in the lemon juice.
Divide the pasta among bowls. Top with more cheese and drizzle with olive oil.