Miss Maudie made a gesture that implied that to her, Jem had matured greatly. Explain?

The children were always treated to their own small, individual cakes when they went to Miss. Maudie's house. In Chapter 21, she invited Jem over. Accompanied by his sister and Dill, Jem went into Miss. Maudie's kitchen. Her gesture? The usual small cakes were waiting, but there were only two...... one for Dill, and one for Scout. Jem, on the other hand, got to share a piece of the adult cake. This was Miss. Maudie's way of marking his maturity.