Mashed Potatoes with Caramelized Onions

In a large skillet, heat oil & butter over high heat until the butter is melted.
Add onions & sugar; cook, stirring often, until the onions are deeply browned, about 20 minutes.
Set aside.
Meanwhile, boil potatoes in water until very tender, 20-30 minutes.
Drain & let cool slightly.
Remove skins from the potatoes & mash.
Stir in salt, pepper & just enough hot milk to make the potatoes fluffy but not soupy.
Stir in the reserved onions & season with additional salt & pepper, if desired.
Serve immediately.