Using a nonroutine problem can be an effective way to encourage students to draw on prior knowledge, work together, and reach important conclusions about the mathematics they are learning. This article discusses a problem on the mathematical preparation of chocolate milk which was adapted from an old book of puzzles (Linn 1969) and has been used for professional development and methods courses, among others. Although it is an interesting problem for secondary students, the author has used it on the first day of a methods course as a way to introduce significant pedagogical ideas. In the chocolate milk problem, the importance of equal parts and equal units are highlighted as students discuss possible solution methods. The successful solution methods can be characterized four ways. The first two methods rely on a deep understanding of two basic yet critical concepts related to fractions--"equal parts" and "equal units". A third solution strategy, called the "numerical approach", involves making the problem more concrete. The fourth approach is more formal and involves algebra. (Contains 4 figures.)