Wash the onions and dry them thoroughly.
Peel them and slice them.
Soak sliced onions in the buttermilk for 15 minutes.
Meanwhile, prepare the flour. Grab a medium-size bowl and Pour the all-purpose flour in it. Add the seasoning such as salt, pepper, garlic powder, and onion powder.
Whisk it to combine thoroughly.
Grab a handful of Onion with your fingers. Shake them to remove excess buttermilk and toss them in the flour mixture until them to coat thoroughly.
Repeat steps 4 to 6 for remaining onions.
Pour the vegetable oil in a frying pan and heat it until it shimmers.
Grab a handful of coated Onion and add them to it. Fry until they turn to golden. It lasts for about 5 minutes.
Gather the fried Onion and place them on the kitchen paper to remove and drain excess oil.
Repeat steps 9 and 10 for remaining coated onions.
Fried Onion is ready to use.
If you want to store it, place it in an airtight container, and refrigerate it.