In a large frying pan or skillet over medium heat, heat two tablespoons of olive oil and fry the crushed garlic until fragrant; add the crushed tomatoes, spices and seasoning and increase heat to high so the sauce is bubbling and reduces to a thick consistency.
Taste the tomato sauce and adjust seasoning and spices as needed, then turn heat to low to simmer or turn off heat until needed.
In a mixing bowl, soak the stale bread slices in the milk until they’ve completely soaked up the liquid. If the bread is too stale you could blitz it with the milk in a blender.
To the same mixing bowl, add the ground pork and ground beef, garlic, onion, egg, spices and seasoning, and chopped celery leaf, and use clean hands to combine well.
Use a tablespoon to scoop out some meatball mixture and check the weight on your kitchen scales – aim for 32 g / 1.13 oz – then roll the mixture between two hands to form into a small smooth meatball. Transfer to a tray then repeat. The mixture should make around 30 meatballs.
In a deep small-medium sized fry pan or skillet, heat olive oil, then transfer enough meatballs to fill the pan, leaving some space between them so they’re not touching, and shallow-fry the meatballs in batches, turning each meatball as needed until brown.
When the first batch of meatballs are brown all over, use tongs to transfer them to the pan of tomato sauce and let them simmer while you fry another batch. Repeat until all the meatballs are fried and brown and are in the pan.
Simmer the meatballs for another 5 minutes then transfer to a bowl and serve with crusty bread, other dishes of tapas and/or a garden salad.