Preheat the oven to 220° C /200° Fan /Gas 7 /425° F.

Cut two pieces of baking paper to fit the bases of two shallow baking trays each 31 x 21 cm. Cook in two batches if you only have one suitably sized tray.

Put the flour, rosemary, garlic powder if using, salt and black pepper in a mixing bowl and stir together. Make a well in the centre.

Stir the water and olive oil together then pour into the centre of the flour mixture.

Start by stirring with a spoon to combine, then switch to your hands to bring together into a dough that leaves the bowl clean.

Transfer to a clean work surface and briefly knead/fold into a smooth ball.

Cut in half (use scales for accuracy) then set one half aside, covered with the upturned bowl so it doesn't dry out.

Lightly flour one of the pieces of baking paper.

Place one piece of dough on it, sprinkle with a little flour, and roll out very thinly (no more than 1-2 mm or the crackers will be hard rather than crispy) until it covers the paper.

Neaten the edges of the dough with a knife, pastry wheel or pizza wheel plus a ruler if necessary.

Cut the dough into squares or rectangles of your preferred size.

Slide the paper and the uncooked crackers onto one of the baking trays.

Prick the crackers all over with a fork.

Put the crackers in the preheated oven and cook until crisp and golden (10-15 min). Check after 8 minutes: crackers at the edges of the tray may cook much quicker, so remove these to a cooling rack and return the rest to the oven.

While the first tray is baking, roll and cut another batch with the remaining dough and cook as above.

When done, crackers should be left on the cooling rack until completely cold before storing in an airtight container. Should keep for 2 weeks.