Peel and thinly slice the onions. You can do this with a sharp knife, a mandolin, or the slicer disk on your food processor, for even-sized pieces.
Fry The Onions:
Heat up about an inch of oil in a large, deep pot. Once hot (over medium heat), add the onion and allow them to fry until browned and crispy (2-4 minutes). Stir occasionally to make sure they're frying evenly.
How to Store Crispy Fried Onions?
You can prepare these crispy onions up to 4-5 days in advance (and store in an airtight container) or up to 2 weeks in advance (stored in the fridge). When using, you can re-crisp them in the oven or Air Fryer at 375ºF/190ºC for just a few minutes.
Freeze: Allow the crispy onions to cool, then place in a freezer-safe bag and freeze for between 4-6 months.