Put the nuts in the bowl of a food processor, saving a handful to serve. Add the garlic, then blitz until you have coarse crumbs. Add the red peppers and tomato purée and blitz again to a rough paste. Add the sourdough and a glug of the oil to loosen the mixture, then blitz once more until you have a slightly smoother paste. Pour the sauce into a mixing bowl and add the cayenne pepper, paprika and some seasoning. Pour in the rest of the olive oil, stirring to incorporate it. Add the vinegar, 1 tsp at a time, until the sauce has the right acidity – it should make you salivate!