Authentic Shiro Wat requires Shiro Powder – a blend of dried, ground chickpea flour (or other legumes) with Berbere and herbs. If you don't have Shiro Powder, you can use plain chickpea flour and mix in Berbere and cardamom. For a creamier flavour, you can add a tablespoon of Niter Kibbeh (for a non-vegan version) or Ghee/vegan butter at the end.
The key is to whisk in the flour gradually to prevent lumps and to cook the Shiro slowly until it achieves the texture of a thick cream/sauce.
In a large pot or Dutch oven, heat the oil (or Niter Kibbeh). Add the finely chopped onion and sauté over medium-low heat for about 5–7 minutes until soft and translucent (traditionally, the onion is braised 'dry' and fat is added later, as with Doro Wat).
Add garlic, ginger, and Berbere spice (and tomato paste, if using) and sauté for another 2 minutes until the spices are intensely fragrant.
Pour in 3 cups of water or broth and bring to a gentle boil. Add salt.
Reduce the heat and begin gradually and very slowly whisking in the Shiro Powder. It is important to whisk constantly (ideally with a wire whisk) to prevent lumps. The Shiro should start thickening immediately.
The Shiro stew should have the consistency of a thick sauce or puree. If it is too thick, add a little hot water. If it is too thin, add a little more Shiro Powder.
Cover and simmer on the lowest heat for 20–30 minutes. Stir occasionally to prevent sticking to the bottom. The Shiro is ready when it is very creamy and 'bubbles' begin to appear on the surface.
Serve the Shiro Wat hot, traditionally straight from a clay pot, into the centre of a large Injera flatbread. It is often served with freshly chopped chillies or green bell peppers to enhance the flavour.