Heat the cooking oil in a wide pot over medium-high heat. Add the sausage and cook, breaking it up with a wooden spoon as it cooks, for 10-12 minutes until well-browned and cooked-through. Season with extra crushed red pepper, if desired. Transfer to a paper towel-lined plate to drain.
Drain off excess fat from the pot, reserving any fond stuck to the bottom of the pot.
Cook the Leeks:
Melt 2 tablespoons butter in the pot. Once frothy, add the leeks and cook for 8-10 minutes until very soft. Season lightly with salt and pepper.
Start the Rice:
Melt the remaining butter in the pot and add the rice. Cook over medium heat, stirring regularly, for 2-3 minutes until just beginning to turn translucent.
Cook the Risotto:
Add 1 ladle of the hot broth (it should be enough to mostly cover the rice in the pot) and bring to a low boil. Reduce the heat to low and stir often for 2-3 minutes until most of the liquid is absorbed. Continue adding a ladle of liquid and stirring for a few minutes until absorbed until 4 cups of the liquid has been added. If you need more liquid, add another cup and allow the liquid to absorb.
Cook the Greens:
Once most of the liquid has been absorbed, add the chopped Swiss chard, sage, and reserved cooked sausage. Cook for 4-5 minutes, stirring regularly, until the Swiss chard is wilted. Taste and season with salt and pepper.
Finish the Risotto:
Turn the heat off the risotto and allow it to rest for 5 minutes. Grate the parmesan cheese into the pot and stir to incorporate.
To Serve:
Divide the risotto between bowls and add a little more parmesan on top, if desired. Enjoy!