Preheat the oven to 450°F (230°C) and place a baking stone, flat iron skillet, or baking sheet in the oven while it's heating.
In the bowl of a stand mixer fitted with a dough hook, combine the all-purpose flour, semolina flour, rosemary, and salt.
Add the water and knead on medium speed for 8-10 minutes, until a smooth dough is formed.
Divide the dough into 12 equal balls (roughly 2 oz/58 g each). Place in a covered bowl, and let rest for 15 minutes.
Brush a work surface with a touch of oil and, working with one ball of dough at a time, roll the dough into a circle as thin as possible, about 8 inches (20cm).
Brush the surface of the dough lightly with olive oil and sprinkle with a pinch of flaky sea salt (if using).
Place the dough directly on the baking stone or pan in the oven and bake for 3-4 minutes, or until bubbled up and golden brown. Flip and cook the other side for another 2 minutes, or until golden.
Let cool on a wire rack while you roll and bake the remaining dough.
Once ready to serve bread up the cracker and serve with cheeses or dips. Store in an airtight container for up to 3 days.