Boil the spinach leaves in 2 cups of water with the salt and onions. After the spinach is cooked, strain and reserve the water. Slightly chop the spinach and set aside. In another pan, heat the lard and flour and cook until golden brown. Remove the pan from the heat and add 1 cup of the spinach water. Mix in the cooked spinach and return to the stove. Heat the mixture to almost boiling point. Just before the mixture starts to boil, blend in the sour cream. Reduce the heat and simmer the mixture for several minutes.
Note: Add more of the remaining spinach water if a thinner mixture is preferred.