I'm not sure why this is "Spanish" as opposed to another version, "Bavarian", which has more cream in it. This recipe comes from a Women's Division of Federated Farmers Cookbook, published in 1965.
600ml of milk ( 1 pint)
20g gelatine
2 eggs
2.5ml vanilla essence
60g sugar
1 Save a small amount of the milk; put the rest in a saucepan together with the sugar and vanilla, and heat through.
2 Separate the egg whites and save for later. Beat the egg yolks with the remainder of the milk and add to the heating mixture.
3 Stir to ensure the sugar is dissolved and bring to near boiling point to thoroughly cook the eggs. Do not actually boil.