Preheat oven to 220°C. Brush a 19 x 29cm (base measurement) slice pan with oil to lightly grease. Combine the bread mix, water, egg and parmesan in a large bowl, and prepare following bread-mix packet directions. Spread the batter evenly over the base of the prepared pan.
Insert the potato slices, about 1cm deep and equal distance apart, in the top of the batter. Push the rosemary leaves into the batter between the potato slices. Drizzle with oil and season with sea salt and pepper.
Bake in preheated oven for 20-25 minutes or until focaccia is golden and a skewer inserted into the centre comes out clean. Remove from the oven.
Use an egg lifter to carefully lift the focaccia out of the pan. Serve warm or at room temperature.