1-1/2 cups (375 mL) flour
1-1/2 tsp (7 mL) salt (approx)
1/4 tsp (1 mL) cayenne pepper
1 bottle (341 mL) beer
1 small Spanish onion
6 cups (1.5 L) vegetable oil for deep-frying
Preheat deep-fryer to 375°F (190°C) and oven to 250°F (120°C).
In bowl, whisk flour, 1 1/2 teaspoons (7 mL) salt and cayenne. Whisk in beer until smooth. Let stand for 15 minutes.
Meanwhile, peel onion. Cut into 1/2-inch (1 cm) thick slices. Separate into rings.
In deep-fryer or deep heavy-bottomed pot, pour in enough oil to come at least 2 inches (5 cm) up side. Heat to 375°F (190°C) or until a 1-inch (2.5 cm) cube of bread turns golden in 20 seconds. Using fork, dip 4 or 5 onion rings into batter; cook in oil for about 1 minute or until golden brown, turning halfway through. Using slotted spoon, transfer to paper towel-lined baking sheet. Keep warm in 250°F (120°C) for up to 1 hour. Repeat with remaining onions.
Sprinkle with salt to taste.