The 300 sandwiches could be a motif that runs through the love story. It might be something that brings the couple together or causes conflict. For example, if one person loves sandwiches and the other has to learn to make them.
Guan Xiaotong's sandwich was a low-calories, high-nutrition food. Guan Xiaotong's fat reduction sandwich was mainly made of lettuce, coriander, cherry tomatoes, cucumbers, eggs, chicken breast, and other ingredients. The preparation method included marinating the chicken breast overnight, then frying it until it was golden yellow; frying the eggs until it was slightly yellow; slicing and striping the cucumber; and finally putting all the ingredients into the bread to make a sandwich. This sandwich was not only nutritious but also low in calories. It was suitable for people who wanted to lose weight and maintain their health. Guan Xiaotong's fat-reducing meal sandwich attracted much attention because she could maintain a good figure and weigh less than 100 pounds, which made people interested in this food. However, other than this information, the search results did not provide more detailed information about Guan Xiaotong's fat loss sandwich.
I could be okay with BL sandwiches in manga if they are well-integrated and add something unique to the plot. But otherwise, I'd rather they weren't there.
The lamb in the story has multiple significances. Firstly, it is a literal object, which is used as the murder weapon. Secondly, it represents Mary's innocence in a way at the start. Just as a lamb is often seen as a symbol of meekness and innocence, Mary was like that before her husband's news. But then it becomes a tool for her to commit a crime, which is a kind of ironic twist on the traditional symbol of the lamb.
It could be a story where the making or sharing of 300 sandwiches is somehow intertwined with a complex love story. Maybe the sandwiches are a symbol of the relationship, like each sandwich represents a different moment or aspect of their love.
It might also be a symbol of power or control. If a character has control over the leg of lamb, whether it's in terms of cooking it, serving it, or using it in some other way, it could show their position in the family or social hierarchy within the story. For instance, if a mother is in charge of cooking the leg of lamb, it could show her role as the provider and caregiver in the family. Moreover, if the leg of lamb is stolen or fought over, it would further emphasize its value as a symbol of power.
I can recommend the following novels about reborn lambs: Reborn in the End of the World: Not a Silent Sheep, Reborn: Not a Sheep of Fate (Gwen's Garden), Always Reborn (a lamb waiting to be slaughtered), The Happy Life of a Reborn Nanny, Reborn like this, right? These novels covered science fiction, modern, urban, and other different topics. The readers could choose to read according to their preferences.