How to Make It
Steep the saffron in the hot water. Heat the olive oil in a large saucepan. Add the onions and cook over moderately low heat, stirring frequently, until soft and golden, about 20 minutes.
Push the onions to the edge of the pan. Add the sausage meat and cook over moderate heat, stirring occasionally, until browned, about 8 minutes. Stir in the chopped tomatoes, saffron water and sage, season with salt and pepper and bring to a boil. Reduce the heat and simmer for 40 minutes; whenever the sauce becomes very thick and begins to stick to the pan, stir in some of the reserved tomato liquid. Season the sauce with salt and pepper.
Bring a large pot of water to a rolling boil. Add salt, then add the malloreddus and cook until al dente. Drain the pasta and immediately add it to the hot sauce; toss well. Stir in the 1/3 cup of grated Pecorino and the basil and serve, passing additional Pecorino at the table.