Prep and chop all onions into thin slices. I did half moons.

Heat a large skillet over medium heat and add butter and olive oil. Once melted, add in sliced onions and cook for 15 minutes, stirring every 5 minutes.

After 15 minutes, add sugar, salt, and pepper. Onions will take about an additional 20-30 minutes to caramelize and get brown. Be sure to stir occasionally. Once onions have caramelized, turn off heat and set aside.

While onions are cooking, bring a large pot of water to a boil. Once boiling add in potato cubes. Bring back to a boil and cook for about 12 minutes or until fork tender. Drain.

Add drained potatoes back to the large pot and use a potato masher or potato ricer to mash. Add in butter, sour cream, and milk and continue to mash until nice and smooth. Mix in salt and pepper.

Pour onions and all of the buttery juice into the potatoes and stir until well combined. Taste and adjust salt and pepper if needed.

Enjoy!