Mix flour and water until smooth. Cover with towel and let set at room temperature for 1-3 days. The mixture should begin to ferment and let a slightly sour smell. You can tell that it is ready when a thick film accumulates on top. It will bubble and look almost brain-like. Skim off and dispose of the dark mold spots. Lightly whisk the batter-it should have the consistency of a thin pancake mix. You're ready to start cooking!
Teff flour is a gluten-free, high-protein flour made from the grains of teff grass, a native Ethiopian grain. Look for it in specialty markets or order it online. Bob's Red Mill makes a nice variety.