Combine yeast and sugar with warm water, then set aside until ready.
Mix flour and one teaspoon of salt in a stand-mixer bowl.
Add three tablespoons of olive oil and the yeast mixture, then mix until you get a smooth dough.
Place it in an oiled bowl, cover it with a kitchen cloth, and set aside until it doubles.
While the potato focaccia dough is proofing, combine the fresh rosemary leaves with two tablespoons of olive oil and salt --- then set aside.
Brush a round pan with the remaining olive oil. For reference, I use a 30-cm or 12-inch diameter pan in this recipe.
Deflate the dough by punching it in the middle and transferring it into the oiled pan.
Use your fingers to spread the dough evenly; rubbing oil on your hands will make it easier.
Cover with the kitchen towel and set aside thirty to forty-five minutes or until it becomes slightly puffy.
Preheat your oven to 220°C (400°F).
Peel and slice the potatoes thinly, then arrange them on top.
Brush with the oil and rosemary from earlier, distributing the rosemary leaves randomly.
Sprinkle with sea salt if you have them on hand.
Place your potato and rosemary focaccia tray in the oven for twenty-five to thirty minutes or until it turns golden (and the potatoes crispy on the edges).
Transfer to a rack and let cool.
Sprinkle with more sea salt, if desired --- slice and enjoy!