For piri piri, preheat a char-grill or barbecue to medium heat. Grill chillies, turning occasionally, until blistered (2-3 minutes). Cool slightly, then peel, discard skin and process with garlic in a food processor until finely chopped. Add egg yolks and lemon juice and process until pale and frothy, then, with motor running, add oil in a thin stream until incorporated. Season to taste. Makes 350ml. Sauce will keep, refrigerated in an airtight container, for 1 week.
Score chicken through thickest parts of thigh and breast with a sharp knife and rub skin with olive oil. Season with sea salt, then grill, skin-side down, until skin is golden and crisp, then turn and cook, brushing chicken occasionally with piri piri, until cooked through (30-40 minutes). Cut into pieces, serve with remaining piri piri.