Boil the potatoes, press or mash them, and let them cool for 10-15 minutes.
Mix all ingredients until all flour is hydrated. Let the dough rest for 15 minutes.
Knead the dough for about 10 minutes. Let it rest for 30 minutes.
Perform a set (4x) stretch and fold and let the dough ferment for 3.5-4 hours depending on ambient air temperature. It shall expand by at least 50%.
Dump the dough from the bowl onto a lightly floured working surface, fold it together, and shape it into a round with a bench knife. let it rest for 15 minutes.
Shape the dough into a Batard, and place it into bread form with size 25x11x7 cm, about 10×4,5×3 inches.Let it proof for about 2 hours, or until the dough reaches the top of the bread form. Preheat the oven in good time before it's time to bake. Starting temperature is 480°F/250°C.
Bake it for 35-40 minutes. You may have to reduce the temperature at the end to prevent the upper surface from getting burnt.
Let the bread cool for a while. Release the bread from the form carefully when you can handle it without burning your hands. Let it cool for an additional hour.