In a mixing bowl, whisk together flour, salt, sugar, baking powder, rosemary, and seeds (if adding).
Drizzle in water and olive oil. Stir until a shaggy dough forms. It’s okay if the mixture seems slightly dry, but if it is very dry and crumbly, drizzle in extra water a teaspoon at a time until there is no dry flour at the bottom of the bowl.
Turn dough out onto lightly floured surface and knead for 3-5 minutes until elastic and firm. It should bounce back when poked. Cover and allow to rest for 20 minutes.
Preheat oven to 40o°F. Line a baking tray with parchment or a silicone baking mat.
Divide dough into 8 pieces and roll out as thin as possible. (The thinner they are, the crispier they will cook up.) If you like, you can roll dough out between 2 pieces of parchment to prevent sticking, or lightly dust your surface with flour.
You can cook the crackers in 8 large pieces, or you can use a knife, pizza cutter, or cookie cutter to cut them to your desired shape before transferring to a lined baking tray.
Sprinkle crackers with salt and gently press down with hands so the salt adheres.
Bake 10-12 minutes, or until crisp and golden brown around the edges.
Remove from oven and allow to cool. They will crisp up further as they cool. If you cooked your crackers in 8 large pieces, you can break them into smaller pieces before serving.