Trim and cut the fennel into 2-3cm wedges (reserving the fronds) and lay out in a roasting tray. Add a splash of oil, season, then roast in the oven for 30 minutes.
Sprinkle over the pine nuts and pumpkin seeds, and pop back in the oven for 8 minutes, until the fennel is cooked through. Remove from the oven and leave to cool for 5 minutes.
Peel the garlic and deseed and roughly chop the chilli. Blitz 2 of the garlic cloves and the chilli in a food processor until finely chopped. Add the fennel, pine nuts and pumpkin seeds, then pulse again until chopped but still quite chunky.
Grate in the Parmesan, then add the breadcrumbs, egg yolk and a pinch of sea salt and black pepper. Pulse until everything just comes together.
Drizzle a roasting tray with olive oil. With wet hands, roll the mixture into about 20 walnut-sized balls, then place on the tray and leave in the fridge for 15 minutes. Preheat your oven again to 200°C/400°F/gas 6.
Drizzle the polpette with oil and bake for 20 to 25 minutes, until the balls are golden and crisp.
While they are cooking, make a tomato sauce. Place a medium-sized, non-stick pan over a medium heat and pour in a glug of oil. Finely slice the remaining garlic clove, finely chop the parsley stalks (reserving the leaves for later) and add both to the pan. Fry for 1 minute before scrunching in the tinned tomatoes.
Fill the tin halfway with water and add, along with a splash of balsamic, then gently bring to the boil. Reduce to a simmer and cook over a low heat for 8 to 10 minutes, until thickened.
Pour the sauce into a food processor and blitz until smooth, then return to the pan and keep warm until needed.
Divide the sauce between plates, arrange the polpette on top, chop and sprinkle over the reserved parsley leaves and fennel fronds, and serve.