Peel then slice cucumber into ¼ inch rounds. 

Add to medium bowl (preferably with a tight lid).

Add sliced onion to bowl.

Lightly salt and pepper, then mix with spoon.

Add sugar, then vinegar, and mix again. 

Add milk then quickly cover and shake bowl, or stir (before milk curdles). 

Taste, then add salt and pepper as needed. 

Can be eaten right away, but better if refrigerated for 2 hours.