Preheat the oven to 175°C (fan 155°C / gas mark 4) and line a baking tray with baking parchment.
In a medium bowl, mix the rice flour, salt and sesame seeds (if using).
Gradually add the warm water, stirring until a shaggy dough forms.
Stir in the vegetable oil or rapeseed oil, then knead the dough in the bowl until smooth and no longer sticky, adding a little more water or rice flour if needed.
Divide the dough into two equal portions.
On a lightly dusted surface, roll one portion out as thinly as possible, about 1 mm thick.
Cut the dough into shapes using a knife, pizza cutter or cookie cutters.
Transfer the crackers to the prepared tray, spacing them apart.
Bake for 15–20 minutes, or until golden and firm to the touch, watching carefully towards the end to prevent burning.
Leave the crackers to cool completely on a wire rack to crisp up.
Repeat the rolling, cutting and baking with the remaining dough.