Roll oranges gently on counter to help release juice. Cut oranges in half, between navel and stem end. Carefully, cut between skin and meat of the fruit, being extremely careful not to cut thru skin. Using your fingers, remove all the meat of the orange and place in a blender. Repeat on all four orange halves. Clean orange halves of all remaining meat and set aside.
Blend the oranges on high speed until they are pureed. Pour into one cup measure (adding water or orange juice to make one cup of liquid).
In medium, microwave safe bowl, bring one cup water to a boil. Add gelatin to water and stir until gelatin is completely dissolved. Add orange mixture to gelatin and stir to blend well. Refrigerate until mixture is almost set.
Using a hand mixer, while beating at medium speed, add vanilla and evaporated milk in a steady stream. Continue beating until gelatin is light and frothy.
Place orange halves in or on top of small bowls (to keep them upright), fill evenly with orange gelatin and level off top (you will have extra orange gelatin). Return orange halves to refrigerator to firm completely.
Add whipped topping to leftover gelatin mixture from Step 5 and beat with hand mixer, on high, until well blended. Spoon into individual dishes and place in refrigerator to firm.