Cut an onion into 4 quarters and slice thin slices off of the quarter pieces, making thin strips of onion. 

Add those thin strips of onion to a medium-sized bowl along with the buttermilk. You just need enough buttermilk so that the onion is submerged. Mix both together and add to the fridge to let the onion soak for 30 minutes to an hour. 

In another medium bowl add your all-purpose flour, salt, garlic powder, and ground black pepper. Mix thoroughly. 

After 30 minutes or so, remove the bowl with your onions and buttermilk from the fridge and place it beside the bowl with the flour. 

Add at least 1 inch of vegetable, peanut, or canola oil to a large pan or pot and place it over medium-high heat. While your oil is heating you can start dredging your onion pieces. grab a handful of onions in the buttermilk and shake off most of the liquid. Add to the bowl with the flour mixture and coat the onions well. Leave the onion pieces in the bowl with the flour until the oil is hot enough.

When the oil has risen to 350 degrees F (176 C) or when tiny pieces of flour sprinkled over the oil start to sizzle upon entry, you are ready to start frying.

Carefully remove some onions from the flour mixture and shake off excess flour. Add to the hot oil carefully and fry in batches for 2 to 3 minutes or until the onions turn a nice golden brown color.

Once any onions are cooked, move them carefully to a cooling rack or paper towels to rest while you fry the rest of your onions.

Add crispy fried onions to a sandwich or enjoy them as a snack.