How to Make It
Whisk all the ingredients in a bowl or a glass jar, cover with something breathable like cheesecloth and leave to rest at room temperature for 2 days. You should see some rising along the way.
Stir the starter. It will smell very grassy, almost in a spoiled kind of way (it might even make you think that it went bad—it likely did not). Resist the urge to throw it away; the smell indicates fermentation, and that's what we're looking for. You also should see bubbles on the surface. Feed the starter with 1/3 cup teff flour and 1/2 cup water, cover and leave to ferment for another 2 days.
The starter may separate into 2 layers at this point—that's fine. Stir it and feed with another 1/3 cup teff flour and 1/2 cup water. Cover and let ferment for at least another 4 hours or overnight. After that, your starter is ready.
In a large bowl, dissolve the starter in water. Add in the flour and whisk into a smooth pancake batter. Cover and let ferment for 5 to 6 hours. Reserve 1/4 cup of starter for the next batch, if desired.
Add in salt, whisk again to dissolve and begin cooking the injera. Optionally, you can add 1/2 teaspoon of baking soda to get more bubbles.
Heat a non-stick pan or skillet with a tight-fitting lid over medium heat. Lightly grease it with vegetable oil using a paper towel.
Add about 1/3 to 1/2 cup of batter to the pan, depending on its size, tilting and swirling to cover the surface evenly. Cook for about 1 minute, until bubbles appear on the surface.
Cover with a lid and steam the injera for about 3 minutes, until the top is set and the bread easily pulls off the pan. No need to flip it over. Remove it and continue with the rest of the batter. It will take a few tries to get the temperature and the cooking time just right.
Keep the cooked injera covered and warm.
Preheat oven to 325°. Snugly arrange the cabbage wedges, carrots and onion in a lightly oiled baking dish. Drizzle olive oil and broth/water over it, followed by salt, cumin, pepper and turmeric, if using.
Cover with foil and braise for 1 hour. Remove the dish from the oven and carefully flip the cabbage, carrots and onion. Braise for another hour. Increase oven temperature to 400°.
Remove the foil and place the dish back into the oven for another 15-20 minutes, until the vegetables are golden brown.
Cook the lentils in plenty of salted water until soft, 15 minutes or so, depending on the type of lentils.
Grind the mustard seeds and peppercorns with a mortar and pestle. Add in the salt and cayenne and pour 1 tablespoon of boiling water over the spices. Add lemon juice and olive oil and stir to combine.
Add the chile or jalapeño into the lentils and pour the dressing over them. Toss well to combine. Adjust salt to taste.
Serve with braised cabbage and lentil salad with warm injera for scooping.