Cook the potatoes in advance and leave to cool. Keep 6 slices to one side for decoration.
Mix the flour and salt in a bowl.
Stir the water into the yeast and add to the bowl.
Blend with a spatula for 2 minutes and add the diced potato. Mix again until you have a smooth dough and finish by kneading with a rolling pin.
Shape the dough into a ball, put it back in the bowl and cover with a cloth. Leave to rest for 45 minutes in a warm place.
Take the ball of dough, divide it into 3 equal pieces and leave to rest, covered, for 10 minutes. Shape into 3 rolls and flatten them out with the aid of a rolling pin. Using a knife, slash the top of the loaves across a third of its length every 2 cms and slightly prise the gaps apart. Place the rolls on 2 baking sheets and leave to rest, covered, for 45 minutes.
Decorate the tops of the rolls with 2 potato slices per roll. Put them in an oven pre-heated to 230°C and bake for 40 minutes.