-Take the peels of 2 large onions (or 3-4 smaller ones).
-Cut in half through the root end of each onion.
-Cut the root end of each onion half off by cutting with your knife on either side to make a V.
-Lay the onion so that what was the root end is facing you, then thinly slice lengthwise.
-Repeat on remaining onion halves.
- Heat 2 TBS unsalted butter in a large saucepan over medium until melted and sizzling. (Using a pan that also has a wide base gives water room to evaporate, allowing the onions to caramelize rather than steam.)
-Add the sliced onions.
-Season with a ¼ tsp sea salt.
-Reduce heat to medium-low and continue to cook onions, stirring every few minutes to prevent them from sticking and coloring too much in any one place, until brown and caramelized, 20-25 minutes.
Let onions cool in the pan, then use or transfer to an airtight container where they will keep for up to a week.