Preheat the oven to 425°F to prepare for baking.

In a large mixing bowl, combine the all-purpose flour, spelt (or whole-wheat/rye) flour, salt, and baking powder. Add ⅔ cup olive oil and ¾ cup water, stirring everything together until it forms a dough.

Move the dough to a clean work surface and knead it briefly to bring it together. Divide the dough into two equal portions.

Roll out each portion of dough directly onto large, rimless baking sheets. Avoid using insulated sheets, as they may prevent the crackers from becoming crisp. Roll the dough very thin—around 3/16 inch or thinner for crispier crackers. Don’t worry about making it perfectly even; irregular shapes are fine.

Sprinkle your chosen toppings, such as sesame seeds, black onion seeds, caraway seeds, or grated cheese, over the dough. Add a pinch of flaky sea salt to enhance the flavor. Use a rolling pin to gently press the toppings into the dough so they stick.

Bake the dough for 18 to 20 minutes, or until the edges are a deep golden brown and the center is lightly golden. Be sure to remove the crackers from the oven once they reach this stage, as overbaking may make them less crisp.

Carefully transfer the baking sheets to wire racks and allow the crackers to cool completely. As they cool, they will become crisp. If they are not as crisp as desired, you can return them to the oven for a few extra minutes.

Once the crackers are cool, break them into smaller pieces as needed. Serve immediately, or store them in an airtight container at room temperature for up to two weeks.