Miss Maudie is one of the nicest and most sensitive people in the whole novel. In many ways she is the female version of Atticus - wise, deliberate, and kind. She baked cakes for the children - Jem, Scout, and Dill. She did so just because she could. It was a part of her benevolence. She expressed kindness because she was kind. Here is what the text says:
Miss Maudie’s benevolence extended to Jem and Dill, whenever they paused in their pursuits: we reaped the benefits of a talent Miss Maudie had hitherto kept hidden from us. She made the best cakes in the neighborhood. When she was admitted into our confidence, every time she baked she made a big cake and three little ones, and she would call across the street: “Jem Finch, Scout Finch, Charles Baker Harris, come here!” Our promptness was always rewarded.
Later on, she baked a big cake for Jem. This was to show that he was growing up. In very subtle ways, she was always teaching the children and encouraging them. Even through baking she was making important points.
There was a big cake and two little ones on Miss Maudie’s kitchen table. There should have been three little ones. It was not like Miss Maudie to forget Dill, and we must have shown it. But we understood when she cut from the big cake and gave the slice to Jem.