Preheat the oven to 190c. Place the peppers on a baking tray and drizzle with oil. Roast until the skins are slightly blackened (about 25-30 minutes)
Meanwhile, place 2-3tbsp oil in a small saucepan and add the rosemary sprigs. Gently warm over a low heat then remove the pan and leave the oil to infuse.
Once the peppers have been roasting for around 15-20 minutes, add the walnuts and stale bread to the tray and leave to toast for the remaining cook time (check often to ensure they don’t burn).
Once the peppers are ready, allow them to cool a little then peel off the skins and discard the core and seeds.
Place the pepper flesh, bread, most of the walnuts (hold some back for finishing), garlic, salt, pepper and a little oil in a food processor and blitz until well combined but not totally smooth (you want a little bit of texture). Taste and add a dash of red wine vinegar and seasoning if needed. Set aside.
Place the pepper flesh, bread, most of the walnuts (hold some back for finishing), garlic, salt, pepper and a little oil in a food processor and blitz until well combined but not totally smooth (you want a little bit of texture). Taste and add a dash of red wine vinegar and seasoning if needed. Set aside.
To serve, spread the romesco over a plate and top with the asparagus. Finish with the remaining walnuts and the rosemary oil/sprigs.