Wash and dry the green beans thoroughly. Trim the stem ends and remove any blemished beans. Pat completely dry with paper towels—dry beans take a crispier batter.

Heat the oil

Pour vegetable oil into a wide, heavy skillet or deep pot to a depth of about 1 to 1 1/2 inches (approximately 1 cup). Heat over medium-high until it reaches 350°F (175°C) or until a small piece of batter sizzles and browns in about 30–45 seconds. If you don't have a thermometer, maintain a steady medium-high heat and monitor closely.

Make the batter

In a bowl, whisk together 3 tbs all-purpose flour, 2 tbs cornstarch, 1/2 tsp baking powder, 1/2 tsp salt, and 1/4 tsp black pepper. In a separate small bowl, lightly whisk the egg white until frothy. Add the cold sparkling water and 2–3 ice cubes to the egg white mixture to keep it cold. Pour the wet into the dry and stir briefly with a fork or chopsticks; do not overmix—the batter should be slightly lumpy and light. If it seems too thick to coat, add up to 1 tbs more sparkling water. Keep the bowl over a second bowl filled with ice to maintain chill if needed.

Coat the beans

Working in small batches (6–8 beans at a time), dip the dried green beans into the batter, allowing excess to drip off. Ensure each bean is lightly and evenly coated but not drowning in batter.

Fry until crisp

Carefully lower battered green beans into the hot oil in a single layer, avoiding overcrowding. Fry for 2–3 minutes, turning once, until the batter is golden and crisp and the beans are tender-crisp. If temperature drops, allow oil to return to heat between batches. Use a slotted spoon or spider to transfer fried beans to a wire rack set over a baking sheet or to a paper-towel-lined plate to drain.

Finish and serve

While still warm, sprinkle the fried green beans with 1 tsp kosher salt and 1 tsp lemon zest (optional). Serve immediately with lemon aioli on the side for dipping.

Lemon Aioli

In a small bowl, combine 1/2 cup mayonnaise, 1 minced/finely grated garlic clove, 1 tbs fresh lemon juice, 1/2 tsp lemon zest, 1/2 tsp Dijon mustard, 1 tsp olive oil, 1/4 tsp salt, 1/8 tsp freshly ground black pepper and 1/2 tsp honey (if using). Whisk everything until smooth and emulsified.

Taste and adjust seasoning: add more lemon juice for brightness, salt for seasoning, or a touch more honey if too tart. Refrigerate for at least 10 minutes to allow flavors to meld; bring to cool room temperature before serving if chilled.

Transfer aioli to a small serving bowl and place alongside the fried green beans for dipping.