Heat the oil: Start by heating 3 inches of oil in a deep pot to 375 degrees Fahrenheit.
Dust the mushrooms: Coat the mushrooms in 1/2 cup of flour, shaking off any excess.
Prepare the batter: In a medium bowl, mix together the remaining cup of flour, beer, salt, pepper, garlic powder, and onion powder.
Batter the mushrooms: Dip each mushroom in the batter, allowing excess to drip off.
Fry the mushrooms: Fry the mushrooms in batches, 4-5 at a time, until golden brown, about 7 minutes per batch.
Drain and serve: Remove the mushrooms from the oil, let them drain, sprinkle with chopped parsley, and serve immediately.