Melt the butter over low heat with the crushed garlic, sliced ginger, cardamom pods, fenugreek seeds and coriander seeds. Simmer very gently 10 to 15 minutes, until the milk solids sink and turn golden.

Strain through a fine sieve into a jar. It keeps in the fridge for a month.

Put the chopped red onions in a large heavy pot over medium heat with no fat and a pinch of the salt. Cook 15 to 20 minutes, stirring every couple of minutes, until they release their water, it cooks off, and they collapse into a soft dark mass. Add a spoonful of water any time they threaten to stick.

Stir in the niter kibbeh and let it melt into the onions. Add the garlic and grated ginger and cook 2 minutes.

Add the berbere and tomato paste and stir constantly over medium-low heat for 2 minutes, until the mixture darkens and turns glossy and the raw spice smell disappears. Keep the heat low, this scorches easily.

Add the sweet potato chunks and turn them gently to coat. Add the rinsed red lentils, the broth and the remaining salt.

Bring to a boil, then reduce to a bare simmer, cover, and cook 30 to 35 minutes. Stir only enough to stop the bottom catching so the chunks stay whole.

It is done when the lentils have disappeared into the sauce and the sweet potato holds its shape but gives instantly to a spoon. If the sauce is thin, mash three or four chunks against the side of the pot and stir them back in.

Taste for salt and add more berbere if you want more heat. Rest off the heat 10 minutes, then serve on injera with sliced green chile and chopped red onion.