Instructions

1. Stir the flax seeds into the water and leave them until the whole bowl has set into a thick gel. This takes longer than it looks, since flax gels from the outside in, and a batch that still runs will not hold a shape.
2. Grate the Parmesan finely and crush the garlic to a paste. Both are being distributed through a gel that barely moves once it has set, so anything in lumps stays in lumps.
3. Fold the cheese, pepper, garlic and sea salt through the gel with a spatula rather than a whisk. A whisk drags the flax into strings and the gel loses its grip.
4. Spread the mixture on a lined sheet to 6 mm with an offset spatula, pushing from one end in a single pass. Working back and forth builds ridges, and a ridge is a thick spot that stays soft while everything around it crisps.
5. Cut the squares while the dough is still wet, taking the knife right down to the liner. Dried flax forms a tough sheet that no knife will part cleanly afterwards.
6. Begin at 63 °C for 45 minutes, which is a short opening burst rather than a stage in its own right. It sets the surface before the cheese has a chance to sweat oil across it.
7. Drop to 46 °C and continue for 6 hours, flipping the sheet onto mesh at the point it will hold together. Until then these dry almost entirely from the top face.
8. Finish with 15 hours at 46 °C. They are done when a cracker breaks with a sharp snap and the edges are no darker than the middle. Cool one first, because Parmesan makes a warm cracker feel firmer than it really is.
9. Keep them airtight in a cool cupboard for a fortnight, or in the fridge for a month. The cheese sets that limit rather than the flax, and flax oil turns quickly enough that stretching it further is not worth the risk.