What do the macaroons symbolize?

The macaroons that Nora eats even though her husband, Torvald, has forbidden her to do so symbolize her rebellion against him and all patriarchal authority. She lies to Torvald not only about the cookies but also about the illegal loan she took out years before so that she could fund their trip to Italy for his convalescence—she forged her father's signature. Later, when Krogstad blackmails her, she believes the law ought to be on her side.
The macaroons also symbolize her husband's attempts to control her. Just as he is unaware of her deception regarding the loan, he believes that she will continue to obey him in all things. He does not see how controlling he is or that his treatment of her is belittling. He treats her just like a child, forbidding her from eating cookies!