Heat the oil in a large saucepan over medium heat. Add the onion and sweet potato; fry gently for 4-5 minutes. Stir regularly until softened.
STEP 3
Add the garlic; fry for another 1-2 minutes.
STEP 4
Mix in the remaining sauce ingredients and 500ml water. Season with salt and pepper. Bring to a boil and simmer for 18-20 minutes until vegetables are soft.
STEP 5
In a large bowl, soak the bread in milk for a few minutes until absorbed.
STEP 6
Add the grated onion, carrot, courgette, minced beef, and the egg yolk. Mix well and season with pepper.
STEP 7
Roll the mixture into 24 small meatballs and place in a shallow ovenproof dish. Bake for 18-20 minutes until browned. Drain any excess liquid.
STEP 8
Remove the bay leaf from the sauce and blitz until smooth using a hand-held blender.
STEP 9
Pour the sauce over the meatballs and sprinkle with cheese. Return to the oven for 20-25 minutes until cheese is melted and bubbling. Serve with pasta or rice.