Pour warm water in a medium size bowl. Add salt and yeast and stir around. Mix in 2 cups of flour. Gradually add more flour until the dough comes together enough for you to start kneading it. Knead for a couple of minutes, add additional flour if it sticks to your hands. Put the dough back in the bowl and drizzle it with olive oil. Work the dough until it’s completely covered in the oil. Cover the bowl with plastic wrap and set it in a warm place for 2 hours.

Meanwhile, you prepare the potatoes. Slice them thin with a knife. Place the slices in a deep plate, drizzle them with salt and cover with cold water for about an hour. Drain the water, rinse the potatoes and pat them dry on a towel.

Preheat the oven to the highest possible temperature (450-500°F). Remove the plastic cover from the dough and start working it with your hands on a slightly floured work surface. Stretch and flatten the dough until you get the desired size and thickness that you prefer and move it to a baking pan covered with parchment paper. 

Brush the dough with a thin layer of olive oil. Cover it with potato slices, onion, rosemary, 3/4 of the goat cheese, salt and freshly grounded black pepper. Drizzle the rest of the olive oil over the pizza and bake for about 15-18 min until the potatoes are golden and the edges are slightly burnt. Sprinkle the rest of the goat cheese over it and serve immediately.