Slice the onions: Trim the tip and end off of each onion. Carefully cut the onions in half and remove the skins. Thinly slice each half, slicing from root to stem. Do your best to cut in even slices for the most consistent cooking.
Heat the pan and fats (olive oil and butter): Heat a large skillet over medium-high heat. Melt the butter with the olive oil.
Add the onions and coat: Transfer all of the onions into the pan and evenly coat in the butter-oil mixture.
Add salt and reduce the heat slightly: After 10 minutes of cooking, sprinkle a pinch of salt over the onions and toss to coat. Reduce the heat to medium.
Allow onions to cook, stirring every so often: Allow the onions to cook, stirring about every five minutes or so, to ensure the onions do not burn or stick to the pan. *Do not over-stir or the onions will not brown. Add a little extra oil or a small amount of water if you find that the onions are burning. Cook for 20-30 minutes, until brown in color and desired doneness, is achieved.
Store onions in an airtight container in the refrigerator for up to one week.
Notes
You do not have to use both olive oil and butter, you can choose to use one of the other. If using just olive oil, start with two tablespoons and go from there.
See the blog post for details on what type of skillet to use.