For spinach balls, wash spinach well and remove hard stalks.
Steam until tender, in a small amount of boiling salted water in a large saucepot.
Drain.
Cool slightly and form into balls about 1 1/4 inches in:diameter.
Push a piece of ham or cheese into center of each ball.
Beat egg whites until stiff; gradually beat in yolks, flour, and salt.
Coat spinach balls with egg batter and fry one layer of balls at a time in hot oil until lightly browned.
Meanwhile, prepare soup.
Heat 2 tablespoons oil in a large kettle.
Add onion and garlic and cook until soft (about 5 minutes).
Stir in tomato paste and stock.
Heat to boiling, reduce heat, and simmer gently about 15 minutes.
Season to taste with salt and pepper.
Serve the spinach balls in the soup.