How to cook
Grind the oat bran and flaxseed in a mill, but you can leave them whole as well.
Mix them with the brown sugar, cinnamon, vanilla. Separately beat the whites into hard snow, and add 2-3 drops of vinegar. To the snowy egg whites, add the other mixture gently with a spatula, being careful not to drop the whites.
Lay out a tray with baking paper and drop a spoon of the mixture in it at a time. Put the biscuits to bake in a preheated moderate (not hot) oven until the edges get a lightly tanned crisp.
The thinner the biscuits with oat bran you make, the crispier they become.