01 - Peel, core, and slice fresh pineapple into 1/2-inch thick rings. Pat slices thoroughly dry with paper towels to ensure batter adheres properly. If using canned rings, drain well and pat dry.
02 - Whisk together flour, cornstarch, sugar, baking powder, and salt in a medium bowl. Pour in cold sparkling water and add egg if using. Stir gently until just combined—small lumps are fine. Do not overmix or the coating will become tough.
03 - Pour vegetable oil into a deep skillet or heavy saucepan to a depth of 2 inches. Heat over medium-high heat until oil reaches 350°F. Use a kitchen thermometer for accuracy, or test by dipping a wooden spoon handle—bubbles should form steadily around it.
04 - Working with one ring at a time, dip pineapple into the batter, turning to coat completely. Lift and allow excess batter to drip off for a few seconds. A thin, even layer creates the crispiest result.
05 - Carefully lower battered rings into hot oil, working in batches to avoid overcrowding. Fry for 1 to 2 minutes per side until deep golden brown and crispy. Remove with a slotted spoon and transfer to paper towels to drain excess oil.
06 - Dust warm fried pineapple generously with powdered sugar. Add a pinch of ground cinnamon if desired. Serve immediately while crisp, accompanied by vanilla ice cream or warm caramel sauce for an indulgent dessert.