Get a fire going on the barbecue and heat the oven to 150C/300F/gas mark 2.
Char the peppers over the flame until their skins are blackened. When cool enough to handle, peel off the skin, remove the seeds and pith and blitz the flesh to a purée.
Spread the almonds and hazelnuts onto a baking tray and toast in the oven for a few minutes until they’re evenly golden.
Heat the oil in a pan and fry the garlic gently in it until golden. Remove from the oil and set aside, reserving the oil.
In batches, pound the nuts to a medium coarse crumb – some can be finer, as this will help to bind the sauce. Then pound the garlic to a smooth paste, and combine with the garlicky oil, pepper purée, passata, paprika, vinegar, saffron and saffron water, and the nuts. The consistency should be loose and dippable. When it’s done, pour into a bowl and keep at room temperature.
Trim the calcots (leaving the roots attached) and soak in salty water (this cleans them and also gets a little salt inside the onion) before throwing over a fire on a rack.
Blacken the outside of the onion and then, when nearly cooked, toss them all together in newspaper and leave them to steam and finish cooking.
Sprinkle the breadcrumbs over the sauce.
Serve the calcots alongside the bowl of romesco. To eat (armed with plenty of napkins), peel away the black outer layer of the calcots (I like to leave a little on) and dip into the romesco sauce. Tip your head back and lower it in. Messy, simple and – importantly – delicious!