Preheat the oven to 375ºF (190ºC) and line a baking sheet with parchment paper.
Place the flour and salt in a large bowl and whisk to combine.
Add the white cheddar and poppy seeds to the bowl. Stir to combine then make a well in the middle of the flour mixture.
Pour in the water and olive oil and stir.
After stirring, the mixture will turn into a shaggy-looking dough. Reach into the bowl with your hands and give the dough a few gentle kneads and turns to incorporate any remaining dry bits of flour.
Place the dough on a work surface and knead it 30 to 40 times, or until smooth. Shape the dough into a ball and cover it with a tea towel for 5 minutes to rest.
With a sharp knife, cut the dough ball into four equal portions. Roll out each of the four smaller balls, on a lightly floured work surface, as thin as you can, about ⅛-inch (3-mm) thick. Add more flour as needed if the dough is sticking.
Slice the rolled dough lengthwise into strips about 1-inch (2-½ cm) wide. Slice the strips widthwise into 1-inch (2-½ cm). The measurements don’t have to be exact. Repeat rolling and slicing the other three dough balls.
Transfer all of the cracker squares onto the prepared baking sheet. Sprinkle the tops of the crackers with flaky salt if you like. Adding salt to the tops is completely optional.
Place the tray of crackers in the preheated oven and bake for 14 to 16 minutes, or until they are golden and crisp. Fully cool the tray of crackers on a wire rack before storing or packaging.