In a large bowl combine the teff flour, all-purpose flour, yeast, salt, and baking soda. Whisk in the warm water and vinegar. Cover the bowl, and place it into a warm place for 1 hour.
Spray a non-stick, 9-inch pan with cooking spray, and heat over medium. Ladle in ¼ cup of the batter, and swirl to cover the surface of the pan.
Cover, and cook for 3 minutes. It will look spongy, and the edges will be browned. Repeat with the remaining batter, and place them on a plate, separating each piece with parchment paper.