How to Make It
Preheat the oven to 300° and line a baking sheet with a nonstick baking mat. In a small bowl, whisk the linseeds with the potato starch and salt. Add the boiling water and whisk until the starch dissolves. Let the batter stand until slightly thickened, about 10 minutes.
Scrape the batter onto the baking mat. Using an offset spatula, spread the batter into a very thin 11-by-15-inch rectangle. Bake for 25 to 30 minutes, until it is very dry and no longer sticky. Let cool completely, about 20 minutes, then break the crisp into large shards and serve within 20 minutes.