"You smell like a mixture of fresh flowers and fresh - bread."
-- Scorpius Malfoy (CC1.10)
Bread Head is what Rose Granger-Weasley calls Scorpius Malfoy in their Potions Class (CC3.14). She is referring back to an earlier time, when he had said that she smelled like bread (CC1.10). Then she had thought he was making fun of her, although he was actually trying to say something nice. As Scorpius now hopes that this is another sign that Rose is coming to like him, he tries to hug her (she kicks him).
Amortentia - a Love Potion that smells like what most attracts you
This is possibly implying that Scorpius has bread on his brain....
The love potion Amortentia will have a different smell to each person, depending on what attracts them (HBP9). It seems that Scorpius, who loves Rose, is attracted by the smell of freshly baked bread. He has many nicknames - this one is almost affectionate.
From the Web
About the play: http://www.harrypottertheplay.com