Heat oven to 200C/180C fan/gas 6. Gently heat the oil in a shallow saucepan then add the onion, celery and garlic. Keep everything sizzling on a medium heat for 15 mins until soft. Tip into a food processor with the rest of the ingredients, except the egg, plus a small pinch of salt, if you like. Pulse until everything is chopped, then add the egg and pulse until combined. Use wet hands to roll the mixture into walnut-sized balls, then place on a baking sheet lined with baking parchment.

Bake in the oven for 25-30 mins until golden and hot through. Will freeze for up to three months; defrost fully before reheating.