Combine in a large pot, potatoes and salted water. Place it on a burner and bring it to a boil.
Test the potatoes for doneness. Once tender, remove from heat and drain.
Combine in a large mixing bowl, first butter, then the sage on top.
Add the potatoes to the mixing bowl and cover it tightly with plastic wrap to trap the steam in.
Hold it somewhere warm for at least 10 minutes, or until needed. The residual heat from the potato steam cooks the sage and melts the butter. This infuses the potatoes with rising sage-scented steam, and then infuses the butter with sage leaves. The longer it sits, the more flavour is leeched from the herb.
Unwrap and toss the contents of the bowl to coat the potatoes evenly with butter as a final touch before serving.