Bring 6 quarts of water to a boil in a large pot, and add 2 tablespoons salt.
Meanwhile, in a 10- to 12-inch sauté pan, heat the olive oil over medium heat until smoking. Add the scallions and garlic and sauté until light golden brown, about 1 minute. Add the tomatoes, fennel seeds, red pepper flakes, and salt and cook, stirring occasionally, until the tomatoes begin to break down, 7 to 8 minutes.
Cook the malloreddus in the boiling water until tender, 6 to 8 minutes; drain.
Toss the pasta into the pan with the tomatoes. Toss until well coated. And sprinkle with the cheese. Serve immediately.
Mound the semolina in the center of a large wooden board. Make a well in the center of the semolina and add the water; salt, and saffron. Using a fork, beat together the water, salt, and saffron, and then begin to incorporate the semolina, starting with the inner rim of the well. As you expand the well, keep pushing the flour up to retain the well shape. When half of the flour is incorporated, the dough will begin to come together. Start kneading the dough, using primarily the palms of your hands. Once you have a cohesive mass, set the dough aside and scrape up and discard any dried bits of dough.
Lightly flour the board and continue kneading for 10 more minutes, dusting the boards with more flour when necessary. The dough should be elastic and a little sticky. Wrap the dough in plastic wrap and allow to rest for 30 minutes at room temperature before using.
Cut the pasta into 4 pieces. Roll each into a 1-inch cylinder, and cut into ¼-inch-thick pieces. Roll each piece down the back of a fork to give it the characteristic ridges, and set aside on a floured surface until ready to cook.