Whenever the Aurors were away from Harry's home, the great Salvator Mundi himself did the cooking for the Potter family.
Cooking was a good way to relieve stress, and compared to Harry, Ginny's skills were lacking by far more than a little.
Molly doted on her only daughter. At home, she never let Ginny do any housework beyond carrying plates, while Harry had been taught by Petunia from childhood how to "fend for himself."
Hermione had not cooked before, but during their adventures, since she was the only girl, the task of cooking fell to her. Harry and Ron were responsible for hunting, as though everyone had forgotten that Harry could cook.
That had truly been an unforgettable, deeply engraved Memory. After the war, they still often gathered together and joked about it.
Hermione's cooking now looked quite decent. After marrying into the Weasley family, Molly had taught her how to cook. Ron was still no good at it. Every Weasley boy had to help their mother with housework, while the twins would make their "dear little brother" choose between doing laundry and sweeping the floor. Every time, Ron ended up doing the work of two people alone.
Traditional views in Britain were generally like this: the kitchen and the home belonged to women, while men were responsible for supporting the family and working. In front of outsiders, even if Ginny was not good at cooking, she still had to go into the kitchen.
Now that the Aurors had left, only familiar people remained at Number 12 Grimmauld Place. Harry thus showed off his cooking skills and prepared a welcome-home meal for his friends returning from afar.
Hermione was helping him. They still used Muggle cooking methods; if they changed the ingredients, it would be no different from Potions class.