In a large mixing bowl add the mince, 70g of the breadcrumbs, the chilli flakes, egg yolk and some salt. Squish everything together with your hands for 5 minutes, then form the mixture into 8 large meatballs. Chill, covered, until needed.
Note: see Notes before following this step. Preheat the grill to its highest setting. Place the whole peppers on a kitchen foil lined baking tray and grill for 15 to 20 minutes, turning halfway, until well blackened. Transfer to a bowl, cover and set aside until cool enough to handle.
Meanwhile, heat the 2 tbsp of olive oil in a large saucepan or casserole. Add the onion and fry over a medium low heat with a pinch of salt for 8 to 10 minutes or until softened and translucent. Add the garlic and fry for 1 minute. Stir through the tinned tomatoes and cook uncovered for 10 minutes. Peel the charred skins off the peppers and discard the seeds. Roughly chop the flesh, add to the sauce then blitz everything with a stick blender until smooth. Add the mascarpone or cream and season, to taste. Keep on a low heat.
Heat the 1 tbsp of olive oil in a large non stick frying pan over a medium high heat. Add the meatballs and fry for 5 minutes, turning regularly with tongs until evenly golden brown. Add the meatballs to the sauce and simmer for 5 minutes, covered.
Preheat the oven to 220C/fan 200C/gas 8. Cook the pasta in boiling salted water for 2 minutes less than the packet instructions, then drain. Toss the pasta with the sauce and meatballs and half of the feta. Tip everything into a large ovenproof dish, scatter over the remaining feta and breadcrumbs.
Bake for 15 minutes, or until piping hot. Scatter over the basil leaves and serve with a salad on the side.