When the poolish is ready, add into the bowl with the poolish the ingredients for the dough: bread flour, wheat flour, warm water & olive oil. Withhold the salt.
Combine all ingredients except for the salt by hand in the bowl, mixing until there is no more dry flour, about 3 minutes. Let the dough rest, uncovered, for 30 minutes.
After 30 minutes, sprinkle the salt over the dough. Squeeze in the salt thoroughly by hand until all the salt is evenly distributed, about another 3 minutes. Cover and let the dough ferment in a warm area of the kitchen for 2.5 – 3 hours or until the dough has doubled in size.
Preheat an oven to 400F.
When the dough has doubled in size, line a half sheet tray or baking sheet with parchment paper and pour half of the olive oil for baking (1/4C) into the tray & rub evenly to coat. Pour the dough into the baking tray & top with the remaining 1/4C olive oil for baking.
Press the dough into the baking tray, spreading it evenly. With the tips of your fingers, press into the dough to dimple it. Sprinkle the flake salt & chopped rosemary over the dough.
Bake at 400F for 20 - 25 minutes or until golden brown. Remove from the tray once baked and allow to cool.