- To make the dough: Mix together the flours, baking powder, salt, coriander, and sugar in the bowl of a stand mixer fitted with a paddle. With the mixer running at slow speed, add the butter. Let the mixer run until the mixture looks like coarse sand.
- Add the egg and water, and continue mixing until the dough begins to come together. Add the chopped fruit and mix just until combined.
- Turn the dough out on a floured surface and pat it into a 9" x 13" rectangle about 1/2" thick. Wrap and chill the dough for 30 minutes, or up to 12 hours.
- To make the the topping: Combine the salt and sugar in a small bowl, and set aside.
- Preheat the oven to 325°F. Line two baking sheets with parchment.
- Remove the dough from the refrigerator and cut it in half. Working with one half at a time, roll the dough 1/8" to 1/4" thick. Trim the edges (save the scraps to re-roll), and cut the dough into 1 1/2" squares or diamonds.
- Transfer the crackers to the prepared baking sheets, and prick each one once with a fork. Sprinkle with the topping mixture, and bake for 16 to 18 minutes, until light brown.
- Remove from the oven and cool on the pan. Store in an airtight container at room temperature for up to 2 weeks.