Soak the chickpeas in enough cold water to cover generously and make a paste up with the flour, salt and baking soda and a little more cold water. Add this to the soaking chickpeas. Leave for 24 hours.
Drain and thoroughly rinse the chickpeas in a colander under cold running water in the sink. Tip them into a large saucepan, cover abundantly with cold water and add the halved onion, sprigs of thyme and olive oil. Do not salt: at this stage it would make the skins tough. Put on a lid, bring to the boil and let bubble away for an hour and a half. At this stage only make you take off the lid to see how cooked the chickpeas are; you may also now add salt. If they're cooked, you should lower in a measuring cup to remove about 2 1/4 cups of the cooking water; otherwise keep going until they're ready.
Once you've reserved your chickpea cooking liquid, drain the chickpeas and remove - with tongs for ease - the bits of onion and thyme. This doesn't have to be ruthlessly carried out, but just get rid of any obvious bits. Once cold you can place the chickpeas in a storage bin, tossing them first in olive oil to prevent drying, until you need them; or else cook them through to the final stage, let them cool and refrigerate them in a covered container or bowl covered with plastic wrap.
Roughly seed and chop the red chile pepper, peel and chunk the onion, press on the garlic cloves to loosen, then remove the skins, add everything, along with the thyme leaves, into the processor and blitz to a pulp. In a large, deep frying pan or casserole - whatever suits - pour the olive oil, and when warm, tip in the pulp from the processor. Sprinkle with salt and cook gently, stirring occasionally, for about 5 to 10 minutes or until soft. Add the chickpeas and turn to coat, then pour in about half the chickpea cooking liquid and bring to a boil. Put on a lid and let cook gently until the chickpeas are hot and soft; you will probably need to remove the lid at the end of cooking to let excess water evaporate. If, however, you run out of liquid before the chickpeas are tender and soused enough, simply add more of the reserved water.
When the chickpeas are ready, turn into a large bowl, or keep in the pan in which you've cooked them. Drizzle with extra-virgin olive oil and stir until the chickpeas are glossy but not too thickly slicked. Sprinkle over sea salt and some thyme leaves if you feel like it (and happen to have some scattered anyway over the work surface - you might well at this stage) or leave them simply oiled and salted.
Recipe courtesy of Nigella Lawson, 2007