Harry wasn't allowed much food as a child. Let alone well-made delicious food. He would crawl back into his cupboard after chores were finished and hope for leftover grilled cheese, his favorite. Toast was good, too, because they sometimes made it just for him. The toast was just for him, and so were the leftovers. Sure, sometimes the leftovers had weird little quirks to them, like many itty-bitty holes, but they were his leftovers.
When he heard of mac 'n cheese he thought the name was silly, but he liked it. Looking at restaurant menus Dudley would bring home, he learned that mac 'n cheese was made with little things called macaroni, that must be why it has the 'mac' part of it's name. When he heard Dudley bellow to his mother about wanting mac 'n cheese again, Harry decided it must be good. The little piggy may not look it, but he had high standards.
One day, Aunt Petunia pulled him aside the morning of Dudley's 6th birthday, telling him that he needed to learn how to make it. She was harsh and critical the entire time, but Harry decided it was easy enough. She let him finish it himself, needing to greet Dudley's friends who had arrived. He finished the mac 'n cheese and took this opportunity to try it himself. He was afraid it'd be a mistake, that he'd feel bad about not being able to have it after, but he was starving and curious about it.
He took a single mac and held it up to examine it. It was orange, but not so much so. It looked easier to chew than anything Harry had had before. He finally put it in his mouth, and the taste greater than anything he'd eaten before. It was different than a grilled cheese. Obviously, he knew that because it didn't have the toasted bread it would, but it was crazy to him anyways. He hoped he'd get a serving, though unlikely.
When he first sat at the Gryffindor table, he was sad to see nothing appearing in front of him, like everyone else. But Ron told him that he needed to think of a food, so he thought of mac 'n cheese. The mac 'n cheese was small, as if the table could sense the way he felt all yucky seeing the large amounts of food on the table. He ate the mac 'n cheese happily, it had been so long.
Hermione made a comment about how she had seen nobody so happy to eat mac 'n cheese before, saying it was an ordinary meal. He took quite the offense to this, and, though not sure how, he must have made it clear. Hermione never jabbed at mac 'n cheese ever again.
He ate only his small mac 'n cheese for the entirety of the next day, every time Hogwarts ate that day. Only when Ron and Hermione told him he should, did he eat something different. Four days each week he'd have mac 'n cheese for lunch, he told his friends about the greatness of mac 'n cheese and how it's superior to the other foods.
His rants of the extraordinary mac 'n cheese only ceased when there were more pressing manners to converse about. He could sadly only get some comments of the food in until they shut him down, rudely enough. He savagely ate his mac 'n cheese the days he couldn't speak of it as it deserved. His love for mac 'n cheese never ended, but as he learned of other food, he stopped eating it as much. He made his birthday mac 'n cheese day, as a solution to his deviance from it as of late.
Now, here in 12 Grimmauld Place, he sometimes eats his macs. At least twice a month. Often times he forgets to eat completely, rotting in bed as what felt like years begins to feel like seconds. His friends still try to remind him of mac 'n cheese day, but he'd rather sleep.