1. Stir the yeast into the water. If using a standing mixer, add all the ingredients into the bowl and mix at high speed until the dough is smooth and elastic; don’t be tempted to add more water so it doesn’t turn too sticky.
2. If kneading by hand, make a mound of flour on a work surface, stir in the oil and add yeast and water bit by bit, kneading into the flour. Continue until you have a smooth and bouncy dough ball.
3. Divide the dough in two, shape each piece into a ball and place in a floured tea towel. Cover and leave to prove for 2-3 hours.
4. To make the tomato sauce, smash the garlic with a knife blade and sweat in the oil, in a saucepan. Add the passata, season with salt and pepper, add half the bunch of basil and bring to the boil. Simmer, half covered, for about 40 minutes to 1 hour until the sauce thickens and reduces by half. set aside to cool.
5. Slice the cheeses thinly and cut or tear into small pieces. Divide in 2 piles, for each scaccia.
6. Generously dust the work surface with flour. Preheat the oven to maximum, with a pizza stone or a heavy baking sheet on the middle rack.
7. Working with one piece of dough at a time, roll it out as thinly as you can; ideally to a rectangle 50 x 40cm or so. If you have a dough scraper, don’t worry if the rolled out dough has stuck to the surface; otherwise make sure you dust both sides liberally with flour.
8. Brush the dough with olive oil; spread a thin layer of tomato sauce all over it and dot with half the cheese allocation for one scaccia. Fold the top quarter (with the help of scraper if necessary) into the middle; fold the bottom one to meet it. Brush with oil, spread with tomato and dot with most of the remaining cheese portion. Now fold the sides to meet in the middle, like a book. Repeat with oil, tomato and remaining cheese, then close one half over the other like closing a book. Pierce the roll in several places to let the steam escape (I forgot, hence the huge air bubble inside).
9. Using a pizza peel or the scraper, transfer the scaccia immediately into the oven, on the stone, leaving space for the other one. Set the timer for 15 minutes.
Proceed with the other scaccia but you might want to wait till the first one is out, not to get confused with timings. It should be puffed up, blistered and deep brown. Cool both scacce on a wire rack. They will deflate as they cool, which is as it should be.
10. To serve, warm (not hot) or at room temperature, cut it in thick slices. Any leftovers will be as lovely on the next day as leftover pizza can be.