Place the potatoes in a large saucepan and add water to cover.
Layer the carrots and the onions on top.
Bring to a boil.
Then reduce the heat to a simmer.
Cook for about 20 minutes or until the potatoes and carrots are fork tender.
Drain, reserving some of the cooking liquid.
Roughly mash the vegetables.
Add butter if desired and salt, pepper and thyme.
Add some of the cooking liquid, just enough to reach your desired consistency (I used 1/4 cup or so) and mash again.
*This recipe brought to you courtesy of Penzey's.*