Place the potato into a saucepan and cover with cold water. Bring to the boil over high heat, then reduce heat to medium and cook for 25 mins or until the potato is very tender. Drain the potatoes in a colander. Use a potato ricer to mash until smooth. Set aside to cool slightly.
In a large stand mixer bowl, combine the 00 flour and 0 flour. Make a well in the centre of the flour and add ¾ of the water, sugar and salt. Place the yeast into the well. Attach the dough hook on the stand mixer and where applicable, secure the clear pouring shield. Mix on the second speed, adding the remaining water as it mixes. Add ½ of the olive oil in a slow stream. Set aside the remaining 30ml of olive oil to top the focaccia. Allow the mixer to knead on speed 2 for 15 minutes or until the dough is elastic, adding the mashed potato in the last 2 minutes of mixing. It should be hydrated and sticky!
Tip: If you don’t have a stand mixer, you can also make focaccia dough in a food processor or kneading by hand is also an option however it is a very sticky dough to work with.
Place the focaccia dough into a large bowl (allowing for the dough to double in size). Cover with a cover with plastic wrap or a damp tea towel. Set aside in a warm, draft-free place for 2 hours or until doubled in size.
Tip: the ideal resting temperature for the focaccia is 28° for best results.
Preheat oven to 210°C fan-forced (230°C conventional/ 446°F /Gas 8). Brush a non-stick shallow baking tray, approximately 40 x 30cm in size (or slightly larger) with canola oil to lightly grease.
Transfer the focaccia dough to the greased baking tray and press into the pan. Set aside in a warm, draft-free place for 1 hour. The focaccia will raise slightly to form a thicker crust.
Use your fingertips to make dimples on top of the dough. Drizzle with the remaining oil, sprinkle over rosemary and freshly grinded sea salt. Arrange the sliced zucchini on top of the focaccia.
Bake on the very bottom of the oven floor for 17 minutes, then transfer to the middle grove of the oven to cook for 5 minutes. Serve warm or at room temperature – buon appetito!