In a large mixing bowl, combine teff flour, all purpose flour, instant yeast, salt and baking soda. Mix well. Stir in apple cider vinegar and warm water. Whisk vigorously into a smooth batter without lumps. Cover and set aside for 1 hour in a warm spot.
Preheat a 9" non-stick or cast-iron skillet on high heat for 5 minutes. Lightly spray the skillet with cooking spray. Pour ¼ cup of the batter on the outside of the hot pan and work in a spiral toward the center. Tilt the pan to fill in any holes. Immediately cover the pan with a loose-fitting lid and let the injera cook for 2~3 minutes.
Injera is done when the top is no longer shiny or wet and feels firm to touch. Transfer the cooked injera to a plate and cover immediately with a kitchen towel or a plastic wrap. Repeat with the remaining batter.Stack the injera on top of each other. Keep them covered to keep them moist and soft.
Buckwheat flour is an acceptable alternative to teff flour in this recipe.
You can use either white vinegar or lemon juice instead of apple cider vinegar.
If you want a slightly more sour taste to the injera, then increase the amount of apple cider vinegar by 1~2 teaspoons.
Make sure that you use a good quality non-stick pan to make the Injera. If not, they tend to stick to the pan.
Leftover injera can be stored well wrapped in the fridge for up to 4 days. Freeze them for up to 2 months. Reheat briefly in the microwave before serving.