Malted milk powder is made from three main ingredients: malted barley, wheat flour, and evaporated whole milk powder.
The malted grain gives the powder its sweet, nutty, toasty flavor. It is used in malted milkshakes, hot drinks, candies such as malted milk balls, and in baking, where it helps dough brown and rise. Commercial brands may add salt, sugar, or other additives, so check the label if you avoid gluten, since barley and wheat both contain it.
Source: Malted milk, Wikipedia