Bring a large pot of water to boil.
Cut rapini into pieces, about 2-3 inches long, stems included. Add rapini to boiling water, salt the water, and boil the rapini until tender, about 12 minutes.
While rapini are boiling: in a small pan, on medium-high heat, add ½ tablespoon olive oil. Once olive oil is hot, add sausages. Sear sausages on all sides, then pierce sausages on one side to release fat. Turn heat down to medium-low and cook sausages until done, about 20 minutes.
In a large frying pan, add 2 tablespoon olive oil. Once olive oil is hot, add garlic.
Once garlic is fragrant, drain the rapini, and add the boiled rapini to the pan. Add salt, pepper and chili flakes. Sauté rapini in the garlic and olive oil for about 5-7 minutes.
At this point, the sausage should be cooked. Slice the sausage into pieces. Add the rapini to a serving platter and top with sliced sausages. Finish with additional chili flakes, if desired.