Thinly Slice the onions.
Add the oil and sliced onions to a large pot or Wok ( I like using my wok for this).
Turn the burner to medium and allow the onions to cook at a simmer, stirring occasionally. Fry till golden and crispy- this will take about an hour.
Strain out the onion pieces (you can keep them and use them as you wish). Allow oil to cool completely before transferring to bottles.
I keep one bottle on the counter for everyday use (keeps for a week or two) and I put the other(s) in the fridge (they will keep for a month).