Cook the potatoes, let cool, and mash.  Season with salt to taste. Leftover mashed potatoes can be used as long as they don’t include any butter or milk.

Mix the flax egg, if using. While the potatoes are cooling, add 1 tablespoon of ground flax meal in a small bowl and mix with 3 tablespoons of water. Allow the mixture to rest for a few minutes to thicken into a gel-like consistency before using. 

Preheat the oven to 425 degrees F. (220 degrees C.) Line a baking sheet with parchment paper.  For crispier bread, place a baking stone on the middle rack of the oven.

Combine the cooled mashed potatoes, egg or flax egg, whole grain spelt or barley, baking powder, and salt in a large bowl. Mix thoroughly until the dough forms a sticky, but manageable consistency.

Divide the dough into four equal portions.  Place one or two pieces on the parchment paper and using lightly floured fingers, flatten each piece into a round disk, about 1/4 inch (0.5 cm) thick.

To prevent bubbling and create an appealing texture, use a fork, pastry wheel, or scoring knife to create unique patterns on the surface of each flatbread.

Place the baking sheet directly on the baking stone in the preheated oven and bake for 15-20 minutes, or until the edges are golden brown and slightly crispy.

The flatbreads are best served warm and topped with butter, cheese, or smoked fish.