To make the pangritata, lightly toast the sourdough. Peel the garlic, then blitz in a food processor with the toasted bread, herbs and walnuts until fine. Preheat a non-stick frying pan over a medium heat, add a drizzle of olive oil, then add the pangritata and fry for around 5 minutes, or until golden and crisp. Meanwhile, bring a large pan of salted water to the boil, then reduce the heat to low and place a large heatproof bowl on top. Add the mascarpone or crème fraîche to the bowl along with the leftover c...