In a large ceramic bowl, stir together the flours and salt. Make a well in the centre of the flour mixture. Sprinkle the sugar and yeast into that well. Carefully pour the water into the well. Let stand until the yeast begins to act, about 5 minutes.
Pour 2 tablespoons of the oil into the well. With a wooden spoon, stir the mixture in the centre of the bowl. Gradually widen the circle of stirring to take in all of the flour at the sides of the well.
Turn out on a floured surface, and knead just until smooth. Keep the dough soft. Pour 1/2 teaspoon of the oil into a clean bowl. Place the dough in the bowl, turning once to oil the top. Cover. Let rise until doubled, 30 to 45 minutes.
Punch the dough down. Use 1 teaspoon of the oil to coat a baking tray, and place the dough on the tray. Gently press the dough out to about 1.5cm (1/2 in) thickness. Pour the remaining 1 1/2 teaspoons oil over the top of the dough. Use the handle end of a wooden spoon to dimple the dough every 2.5cm (1 in). Sprinkle with the rosemary and the cheese. Place in a cold oven on the centre shelf. Place a flat pan of hot water on the shelf below the bread. Let rise until doubled, 20 to 25 minutes.
Preheat the oven to 190 C / Gas mark 5.
Bake the focaccia for 20 to 25 minutes, or until browned on top. Remove from the tray, and cool on a wire rack. Serve warm.
This focaccia is truly delicious. I topped it with cheddar and chopped chillis. The "hot water in a cold oven" trick seems to be the key to getting it really tender and moist. I left the water in the oven even as focaccia was baking. - 14 Jul 2008