Mix flour with salt in mixer bowl. Add sugar, yeast, and basil leaves and mix together.
Attach dough hook, turn machine on low and gradually add warm water until dough starts to come together. You may not need all the water!
Increase the mixer speed and knead vigorously until the dough is smooth, springy and soft
Rub inside of bowl with olive oil, replace dough, cover with oiled clingfilm and leave to rise in a warm place until at least doubled in size, about 2 hours.
For the topping add basil leaves and tomatoes in a large bowl. Season with salt and pepper and add chilli flakes if using. Add garlic and olives and mix well.
Heat 2 tablespoons olive oil in a large frying pan on low heat. Add onions and sauté gently until nicely soft, gently tip in basil and tomato mixture, stir continuously, increase heat to medium. Add balsamic and white wine vinegar and cook further until reduced slightly for 1 to 2 minutes. Empty into a bowl and leave to cool.
Punch down the risen dough and knead gently on a surface lightly dusted with flour. Divide into 4 equal pieces.
Lightly grease 4 shallow 20cm (8 in) cake tins.
Gently spread out dough using finger tips to make deep wells. Place in tin and spread gently to the edge, continue same way with the other 3 pieces.
Divide basil mix evenly between dough and spread gently. Top with sprinkling of cheddar to taste preference, or other type of hard cheese of choice. Add any juices as well. Leave to prove for further 15 to 20 minutes, no need to cover.
Pre-heat oven 200 C / Gas 6. Place oven shelf just above centre.
If the oven has room, place all the tins in the oven at once and bake until bottom sounds hollow when gently tapped, about 20 minutes. Otherwise bake 2 at a time.
Leave to cool in tins for 10 to 15 minutes so dough will absorb all the lovely juices. Remove gently, you may need to run a small spatula around the rim to loosen the cooked focaccia, then gently place on cooling rack. Cut into wedges and enjoy.