In a small bowl combine yeast, sugar and water. Set aside in warm place for 10 minutes
Stir together flour and salt in another bowl, add the olive oil and yeast mixture. Knead by hand.
Place the dough on a floured surface and knead until soft and elastic (10 minutes).
Place the ball of dough in an slightly oiled bowl, cover and let the dough rise in a warm place until volume has almost doubled (1 hour at least)
Preheat the oven on high heat.
Wash the potatoes and Jerusalem artichokes. Cook the potatoes in salted water until tender. Drain, let cool and slice them finely and evenly. Do the same with Jerusalem artichokes.
Line parchment paper on the baking tray.
Knead the dough again then roll out on a floured surface and form a rectangle. Sprinkle some olive oil, sea salt and pepper on the dough. Place slices of mozzarella on the flatbread then lay the new potatoes and Jerusalem artichokes on top. Season again.
Carefully transfer the flatbread to the baking tray. Bake for 10-12 minutes until dough is crispy and golden. Take out of the oven, garnish with arugula and some olive oil.
Serve with a side salad