Bring the potatoes to the boil in a large pan of water and then simmer for 15 minutes, or until tender.
Drain the potatoes in a colander over a bowl and reserve the cooking liquid. You will need to measure out 130ml/4fl oz of liquid. Put the potatoes back in the hot saucepan for a few minutes to dry out.
Place the flour, yeast, salt, sugar and rosemary in a large bowl and mix until evenly distributed. Mash the potatoes with the olive oil, add to the flour mixture and mix well.
Add the reserved potato water gradually. Once the mixture is well combined and has come together into a ball, tip out onto a clean work surface and use a little olive oil to help with the kneading.
Knead for around 10 minutes, or until the dough feels smooth. Place into a lightly oiled bowl and cover with oiled cling film and leave to prove in a warm place for at least an hour.
While the dough is proving, clean and half the new potatoes and cook until par-boiled in salted water. Keep to one side until needed for the topping.
Preheat the oven to 220C/425F/Gas 7.
Generously grease a baking tray and tip the dough out into the tray - it will be quite wet still and very elastic. Carefully and gently spread the dough out using your fingers to fit the tin. Do this gradually over 30 minutes, then drizzle over more olive oil and top with the rosemary springs, new potatoes, gorgonzola and sea salt to taste.
Bake for 25-30 minutes until golden-brown.