Heat oven to 180C, and line two baking trays with baking paper.
Combine all the dry ingredients, plus the orange zest, in a large bowl. Mix well with a balloon whisk to distribute evenly.
Make a well in the centre and pour in the eggs, orange juice and Cointreau, then mix until it comes together, using wet hands to form a stiff dough. If it's too dry, add a little more juice.
Divide the mixture into 4, forming each piece into a 20 cm log, place on the baking sheets, well spaced, and pat down to flatten a little.
Bake for 30-35 minutes, until golden brown, then remove from oven and allow to cool just a little, until you can handle them. Using a serrated bread knife, slice each log into 1.5cm slices and spread out evenly on the trays.
Return to the oven and bake a further 10 minutes, turning each slice over halfway through. Do not allow them to brown any further, so turn the oven down a little if necessary.
Once done, cool on a wire rack and store in an airtight container.