In a food processor, add the einkorn flour, hard red wheat flour, salt, baking powder, and cane sugar. Pulse a few times until evenly combined.
Add the cold, cubed butter and avocado oil. Pulse until the mixture becomes crumbly and resembles coarse sand with small pieces of butter throughout.
With the food processor running, slowly drizzle in the ice-cold water. Add just enough for the dough to come together into a soft, slightly sticky dough. Stop mixing as soon as it forms to avoid overworking it.
Use a spatula to scrape the dough onto a lightly floured surface. Gently shape it into a smooth rectangle, then wrap tightly in plastic wrap and refrigerate for 30-60 minutes to firm up.
Place the chilled dough between two sheets of parchment paper and lightly sprinkle with flour. Roll it out evenly until it is about 1/8 inch thick.
Remove the top layer of parchment and use a fork to poke holes all over the dough. This helps prevent the crackers from puffing while baking.
Cut the dough into long strips, then cut across into your desired cracker size. Don’t worry about making them perfect.
Transfer the crackers to a parchment-lined baking sheet, spacing them slightly apart. Brush the tops lightly with egg wash and sprinkle with mineral salt.
Bake on the middle rack at 400°F (200°C) for 12 to 14 minutes, or until the crackers are golden brown around the edges. Watch closely toward the end, as they can brown quickly.
Let cool on the pan for a few minutes before transferring. They will crisp up more as they cool.