[m] It's a oneshot japanese manga that didn't have colour.
The main character is female and the person she was pursuing is a male schoolmate.
The setting is a high school.
The main character gives up on giving him the chocolate and eats it only for him to use tasting it as an excuse to kiss her. OR The main character successfully gave the chocolate to him only for him to eat it and then kiss her as an excuse to give her a taste (am not 100% sure it's the first one)
I think it was shoujo.
The kiss happened around the end an was quite impactful.
I really wanna reread it, I really did enjoy it.

There is a scene in Lip Cream's Chocolate Cake, Shooting Star that is really similar to this except...

the male love interest steals a kiss after helping her make a chocolate cake asking to taste "one more." She is planning to give the chocolate to someone else, I think.

http://i.imgur.com/LxhWm.jpg (will reformat this some day…)