Peel the onions and trim off the ends. Cut the onions crosswise into 1/2 inch thick slices. Separate the slices to create rings. Remove the smallest rings and reserve for a different use.
Place the buttermilk in a large bowl. Add the onions and soak for one hour.
Heat 3 inches of oil in a deep pot to 375 degrees F.
Place 3/4 cup of flour in a bowl.
In a medium bowl, mix together one cup of flour, beer, salt, pepper, and garlic powder.
Remove each ring from the buttermilk, letting the excess drip off. Coat each ring in flour, then dip the rings into the batter.
Fry 6-8 rings at a time until golden brown, about 3-4 minutes.
Repeat the process with the remaining onion rings.
Sprinkle with parsley, then serve immediately.