Add the stock to a saucepan, and heat gently on low heat.
Heat the olive oil in a heavy based pan over a medium heat. Add the onion, pumpkin & garlic, and cook until softened – approx 8-10 minutes.
Add the rice and stir constantly for 2-3 minutes until the rice starts to turn translucent.
Reduce the heat to low, then add the stock one ladle at a time, stirring constantly until all the liquid is absorbed and the rice is cooked (but not stodgy).
Stir through the grated cheese, then leave to completely cool.
Put the flour, egg and breadcrumbs in separate dishes, then roll a ball of the rice mixture in the flour (shake off any excess), followed by the egg and then breadcrumbs.
Heat the sunflower oil in a pan, and fry the arancini balls in batches for approx 4 minutes or until golden brown.
Serve with your favourite dip (we went for a spicy tomato dip, but Salsa Verde or Tomato Salsa also work really well).