Heat a large heavy pan over medium heat, add oil, and swirl to coat the pan.
Add onions, stir to coat with oil. Saute over medium heat, stirring frequently, until golden.
Remove from heat and let cool.
Once cool, package in a plastic freezer bag. Flatten and push air out, so the onion freezes as a thin sheet, and you can easily break off the amount you want at any time.
Notes
Use the sauteed onion in slow cooker or pressure cooker recipes. or just to get a meal on the table more quickly and easily!