In a bowl whisk beer into flour until batter is smooth and whisk in parsley. Let batter stand 30 minutes and stir in 3/4 teaspoon salt. Cut onion crosswise into 1/2-inch-thick slices and separate slices into rings. In a large deep skillet heat 1-inch oil to 380 degrees F. Working in batches of 4 or 5 onion rings, drag rings through batter to coat completely, letting excess drip off, and fry, turning, until golden, about 1 to 2 minutes. With tongs transfer rings as fried to paper towels to drain and season with additional salt.