Cut the onions into strips, uniform in size.
Heat a large skillet over medium high heat.
Once the skillet is hot add the butter and olive oil.
Once the butter is sizzling add the onions and stir to combine.
Let the onions sit, uninterrupted, for about 5 minutes.
Turn down the heat to medium and stir to combine.
Repeat for about 20 minutes.
If needed, add an additional tablespoon of butter or olive oil.
If you see the onions are starting to burn, turn down the heat to medium low.
Continue to stir every 5 minutes until you're left with golden caramelized onions.