In a large skillet over medium heat, melt the butter and then stir in the olive oil.
Add the onions to the pan and cook for 3-4 minutes, stirring occasionally.
When the onions are softened and beginning to caramelize, stir in half the cabbage. Cook the cabbage for 4-5 minutes, stirring occasionally, until wilted.
Add the remaining cabbage to the pan and stir to combine. Cook for an additional 4-5 minutes, stirring occasionally, until wilted and beginning to caramelize.
Season with salt and pepper. Cook for an additional 4-5 minutes.
Remove from the heat and stir in the sour cream. Top with bacon or pancetta, if desired.
Serve immediately.
