There are a couple great things about butter. The wonder of butter as an emulsion enables us to thicken sauces, smooth other emulsions, and add richness in many forms. Butter along with gentle heat also gives us the greatness of brown butter: nutty, toasty, aromatic, and deep. Commercially produced butter must contain at least 80% butterfat, but is usually higher. The remaining composition of butter is 16-17% water and 1-2% milk solids other than butterfat. Therefore, the deep savory notes of brown butter are limited to the 1-2% milk solids.
Dry milk powder comes into play here. Essentially dry milk are the solids that have remained after all the water has been evaporated. In addition to low heat and butter, dry milk solids increase the total solids without adding more liquid or butterfat, as a result increasing overall flavor when browned.
Reconstituting dry milk powder to make milk is gross and terrible. Making milk from powder used to be a last resort for making cereal for breakfast when I was young, we would rather use juice or any other liquid available... I don't do it anymore. At least there is a good use for it now.