Symbolism, Imagery, Allegory
It becomes pretty clear over the course of the book that one word that can be used to describe his home life is dysfunctional. Or to be fair, we could just say that to hear him describe it, his childhood in that house was less than idyllic. One way the author chooses to show us the disparities between his home and the Hempstock's relative excellence is by describing the foods that are served in their respective kitchens.
At home, the foods he mentions are plain, overcooked, and supremely unsatisfying: The burnt toast that his father offers every Saturday morning out of a stubborn refusal to buy a toaster; the meatloaf that the boy is convinced Ursula Monkton concocts to poison him; or the fact that he says this at one point:
We picked some pea pods, opened them and ate the peas inside. Peas baffled me. I could not understand why grown-ups would take things that tasted so good when they were freshly-picked and raw, and put them in tin cans, and make them revolting. (10.67)
On the other hand, over at the Hempstock's they're always stuffing him full of rich, delicious meals that sound absolutely delightful:
She gave me a china bowl filled with warm porridge from the stovetop, with a lump of homemade blackberry jam, my favorite, in the middle of the porridge, then she poured cream on it. I swished it around with my spoon before I ate it, swirling it into a purple mess, and was as happy as I have ever been about anything. It tasted perfect. (2.64)
This pattern is repeated throughout the book: he is given something at home that is flawed and unsatisfying, and then at the farmhouse he is given something that is blissfully delectable. Used as an extended metaphor, the food represents his ongoing dissatisfaction with his home life. He doesn't feel like he fits in with his family, but when he's over with the eccentric ladies down the road he's happier than a pig in… mud. Mud was the word we were going to use.