What a good read. As therealsnape says, you do a fine job of making both characters understandable and complexly human at the same time that you don't excuse them or paper over their flaws. I think the food motif works very well, too, as a barometer of Petunia's changes and the growth of her relationships with both the wizards in her life, Wesley and Severus. The reborn lily becomes a metaphor for the entire story: all the main characters are withered; all come back to life. Petunia and Severus both get Lily back, metaphorically speaking; they renew themselves; they create a new life.
You've created such a full and detailed world here; great job.
I'd write a longer review, but you've made me too desperate for roast beef on rye with good mustard and sharp cheddar. I'll be in the kitchen. . .