What is 1 cube of mayonnaise?

"1 cube of mayonnaise" is not a standard measurement or unit. Mayonnaise is a viscous liquid, not a solid that can be cubed.

Perhaps you are thinking of:

* A tablespoon of mayonnaise: This is a common measurement used in recipes.

* A dollop of mayonnaise: This is a less precise but still common way to describe a small amount of mayonnaise.

Please clarify your question if you are referring to something else.