Boil potatoes until tender. Dissolve yeast in warm water in large bowl and then mix potatoes, flour, 2 tsp salt, dissolved yeast, and 1 tbsp olive oil until blended. Set aside to rise until double (about 30 minutes). Preheat oven to 350 deg F. Coat a baking pan with remaining oil, place dough in pan and turn to coat dough with the oil, gently push down and shape out into a rectangle, making indentations with your fingers. Arrange the tomato slices on top and press slightly. Sprinkle rosemary and salt over top. Bake until golden brown, about 45 minutes.