Preheat the oven to gas 4 / 180C / 350F and line 2 baking sheets with parchment paper
Put the flour, baking powder, butter and the 1/2 tsp salt in a bowl and cut the butter in until the mixture resembles crumbs
Add 4 tbsp of the water and knead the dough together with cold hands. Add the last tbsp of water if required and if anymore is needed add a tsp but you want the dough to be soft, not sticky
Divide the dough in half and roll out both pieces on top of the parchment paper from the baking sheets. This makes lifting it easier. The 2 dough rectangles should measure around 25cm x 15cm each and should be very thin
Brush the dough with water and sprinkle a 1/2 tsp salt over each. Prick all over with a fork
Instead of the salt topping you could use fennel seeds, sesame seeds, poppy seeds, onion powder, finely shredded cheese or nutritional yeast flakes etc
Using a knife or pizza cutter, cut each rectangle into 8 smaller ones and spread out a little on the trays
Bake for 10 - 15 minutes until dry but still pale/very lightly golden. They'll harden as they cool on a wire rack
Store in an airtight container and they'll keep well for up to 3 days
