In a large mixing bowl, combine the teff flour, all-purpose flour, and salt.
Gradually add the water, stirring continuously until you have a smooth batter.
If using, dissolve the active dry yeast in a little warm water and add it to the batter. Stir well.
Cover the bowl with a cloth or plastic wrap and let the batter sit at room temperature for 24 to 48 hours. The batter should develop a slightly sour smell and may bubble slightly. This fermentation process helps develop the characteristic flavor of injera.
Preheat a non-stick skillet or a large, flat griddle over medium heat.
Lightly grease the skillet with a small amount of oil or non-stick spray.
Pour a small amount of batter onto the hot skillet and quickly swirl to spread it into a thin, even layer. Cook until bubbles form on the surface and the edges start to lift, about 2-3 minutes. Do not flip; injera is traditionally cooked on one side only.
Remove the injera from the skillet and place it on a plate. Cover with a cloth to keep warm while you cook the remaining batter.
Injera is typically served as a base for various stews and salads.
Enjoy your meal!