What do Ella and Char write about in their letters to each other? How does Char always close his letters, and how does Ella respond?

In the letters between Ella and Char, they write about all kinds of things and share many soul secrets though Ella never tells Char about her curse or that she is living as a servant. In Char's letters he always closes by asking Ella if she is old enough to marry yet, and Ella always gives a silly answer unsure whether he is joking or not.