Slice off ends of onions and peel off the skins. Slice into 1/2-inch rings. Place rings in a bowl of ice water and let sit. In separate bowl whisk together beer and flour. Season with salt, cayenne, and a dash of Tabasco. Whisk together. Dry onion rings on paper towels then dip into batter. Heat oil in a large kettle to 375 degrees. Dip dried onion rings in batter. Fry onion rings until brown and crispy. Serve.