Combine all the ingredients in a large mixing bowl. Whisk vigorously into a smooth batter, 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 ¼cup 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.
Stack the injera on top of each other. Keep them covered to keep them moist and soft.
Buckwheat flour can be used instead of Teff flour.
Apple cider vinegar can be substituted with either white vinegar or lemon juice.