01 - If using fresh pineapple, peel, core, and slice crosswise into ½-inch thick rings. Pat thoroughly dry with paper towels to remove excess moisture for better batter adhesion.
02 - In a medium mixing bowl, whisk together all-purpose flour, cornstarch, granulated sugar, baking powder, and salt until well combined. Pour in cold sparkling water and add egg if using. Stir gently until just combined—small lumps are acceptable. Avoid overmixing to keep the batter light.
03 - Pour vegetable oil into a deep skillet or saucepan to a depth of about 2 inches. Heat over medium-high heat until the temperature reaches 350°F. Use a kitchen thermometer for accuracy, or test by dropping a small amount of batter—it should sizzle immediately and rise to the surface.
04 - Dip each pineapple ring into the batter, turning to coat completely. Lift and allow excess batter to drip off for a few seconds. The coating should be thin and even for optimal crispiness.
05 - Carefully lower battered rings into the hot oil, working in batches to avoid overcrowding. Fry for 1 to 2 minutes per side until golden brown and crispy. Using a slotted spoon, transfer to a plate lined with paper towels to drain excess oil.
06 - Dust warm fried pineapple rings generously with powdered sugar. Add a light sprinkle of ground cinnamon if desired. Serve immediately while hot and crispy. Accompany with vanilla ice cream or drizzle with warm caramel sauce for an indulgent dessert presentation.