To make the sauce, toast the walnuts in a large heavy frying pan, stirring over a medium heat for about 5 minutes until the walnuts are golden brown. Remove from the pan and leave to cool.
Set aside a few walnuts to use as garnish, then grind the remainder in a food processor.
In a medium bowl, combine the garlic, tahini, and lemon juice and season to taste. The paste will be very thick at this stage, so add 4-5 tablespoons of water and beat with a fork until you have the consistency of very thick double cream, adding more water as needed. Add the ground walnuts to the tahini and refrigerate until ready to use.
To make the meatballs, combine the minced veal and chicken in a bowl, then add the onion, garlic, sour cherries, pine nuts, paprika, allspice and cinnamon. Mix well, then stir in the beaten egg white. Add the fresh herbs and salt and pepper to taste and mix thoroughly.
Shape the mixture into balls the size of golfballs. Heat the oil in a large frying pan. Fry the meatballs a few at a time, turning occasionally, until cooked through and brown on all sides, about 10 minutes per batch. Keep the cooked meatballs warm while you fry the remainder.
To serve, garnish the tahini and walnut sauce with the reserved whole walnuts, and serve with the hot meatballs and some crusty bread.