In a small bowl combine psyllium husk with water and set it aside for about 30 minutes. It should create gel-like consistency.
Meanwhile, in a large bowl combine buckwheat flour, corn flour, rice flour, cornstarch, baking powder, and salt. Next, add psyllium gel and combine. The dough should be very sticky - this is how it should be.
Prepare a baking pan lined with parchment paper and create a loaf using your hands and cornstarch.
Cut the bread on top a few times to prevent the bread from cracking.
Bake at 400F (200°C) for 1 hour.
When the bread is completely baked, wait until it's cold and then serve. Don't slice the bread when it's warm.
