Force ground pork and onion through the medium blade of a meat grinder three times into a large mixing bowl.
Or, have meat market grind the pork three times; mix in the minced onion.
Mix in flour.
Add milk, about 4 tablespoons at a time, beating thoroughly after each addition.
Mix in a blend of salt and pepper.
Beat egg whites to stiff, not dry, peaks and fold into meat mixture until blended.
Thoroughly heat butter, all at one time, in a large skillet.
Spoon meat mixture by tablespoonfuls (keeping oval shape) into hot butter.
Fry until browned on all sides.
2 1/2 dozen meatballs
Note: If using an electric blender, pour half of the milk into the container, add the quartered onion, and about 1/4 of the meat.
Blend, continuing to add milk and as much meat as container will hold.
Empty into a large mixing bowl.
Put milk and remainder of meat into container and blend until smooth.
Empty into bowl.
Mix in flour and seasonings; proceed with steps 3 and 4.