Heat the oil over medium heat in an extra deep 12-inch nonstick skillet that has a lid. Meanwhile, scrub the potatoes (leave the skins on) and cut into roughly 3/4-inch cubes, adding them to the pan as you cut. Raise the heat to high, then cover and cook for 3 minutes to brown the cubes slightly, uncovering occasionally to stir. While the potatoes cook, begin to peel and chop the garlic. Add the sausage to the skillet and stir constantly for 2 minutes with a spatula to break up the chunks. Once the sausage is broken up, cook until the potatoes are golden brown and the sausage is brown, 7 to 9 minutes more, stirring occasionally. Meanwhile, finish chopping the garlic and add it the pan. Add the rosemary and sugar and stir well. When the sausage is done, stir in the tomatoes with their juice and cook until about half of the juice evaporates, 2 to 3 minutes, and serve.