Cook pasta according to package directions until al dente.
Heads up, you will need to use about 1/2 cup of the starchy cooking liquid for the sauce before you drain the pasta.
In a small mixing bowl, combine the ricotta cheese, lemon zest, salt, and a lot of freshly ground black pepper.
Reserve the ricotta mixture on the countertop and let it come up to room temperature The flavors of the cheese and lemon will develop as the cheese warms up.
Preheat a large skillet over medium-high heat with the EVOO.
Add the sausage and break it up with the back of a wooden spoon into a small bite-size pieces.
Really go at breaking the meat up; it will make a difference in the end.
Cook the meat until brown, about 4 to 5 minutes.
While the sausage is browning, prepare the broccoli.
Cut the broccoli tops into small florets. Remove the fibrous outer layer of the stem (just square it off using your knife), then thinly slice the tender center portion of the stem.
Once the sausage is brown, remove it to a paper-towel-lined plate.
Return the skillet to the heat and add all of the broccoli and the chopped onion. Spread the veggies out in an even layer in the pan, season with some salt and pepper, and let the broccoli brown up a bit before stirring, about 2 minutes.
Add the garlic and red pepper flakes and continue to cook 2 minutes more.
Add the sausage back to the skillet along with the chicken stock.
Ladle in some cooking water from the pasta and bring up to a simmer.
Cook until the broccoli is tender and the liquids have reduced slightly, about 2 minutes.
Add the lemon juice, parsley, and cooked, well-drained pasta.
Toss to combine and simmer 1 last minute to allow the pasta to soak in the sauce and flavors.
Turn the heat off, add the grated cheese, and toss to combine.
To serve, place a large dollop of the pepper-lemon-ricotta mixture into each of 4 shallow bowls and bury it with the hot pasta.
Once you are at the table, mix it up with a fork to distribute the ricotta cheese. Serve with extra grated cheese.