Mix yeast and sugar and sprinkle on top of lukewarm water in a jug. Rest for 10 minutes or until frothy.
Mix flour and salt in a mixing bowl. Make a well in centre and add the dissolved yeast mixture, olive oil and mix well with a wooden spoon.
Knead dough lightly on floured surface until smooth and supple. Cover and rest to rise for 45 minutes.
Leaving skin on, pierce potatoes twice, both sides and microwave whole on high for 5 minutes. Turn and microwave for a further 3 minutes. Rest to cool.
Place dough on a floured work surface, knead lightly before rolling out thinly.
Cut out 8 leaf-shaped pieces approximately 12cm long. Using your fingers, make the middle thinner than the edges. Place on a baking tray lined with a baking paper.
Mix fetta, lemon juice, salt, white pepper and spread thinly on flatbreads. Peel and thinly slice the cooked potatoes and arrange on top of the cheese. Top with pecorino, rosemary leaves and freshly ground pepper.
Grill under medium heat for about 15 minutes,until golden brown.
TIP: Cook the potatoes the night before or use sliced leftover roast potatoes.