Rinse prawns under cold water and pat completely dry with paper towels. Trim any remaining shell and remove the vein if not already removed. Place prawns in a medium bowl and season with kosher salt and white pepper; toss to coat.

Batter

In a separate bowl, whisk the egg white until slightly frothy. Add cornstarch and all-purpose flour to the egg white and stir until you have a slightly thick, even batter that will cling to the prawns. Batter should be thick but pourable; if too thick, add 1 teaspoon cold water.

Heat oil

Pour vegetable oil into a deep skillet or medium saucepan to reach about 1.5 inches depth. Heat oil over medium-high heat to 350°F (175°C). If you don't have a thermometer, test with a small drop of batter — it should sizzle and rise steadily.

Fry prawns

Working in batches to avoid crowding, dip each prawn into the batter, letting excess drip off, then gently lower into hot oil. Fry until golden and crisp, about 2–3 minutes per side depending on size. Use a slotted spoon to transfer fried prawns to a wire rack set over a baking sheet or to paper towels to drain. Keep warm in a 200°F (95°C) oven if desired while frying remaining prawns.

Walnut Glaze

Toast walnuts

While frying (or ahead of time), toast the walnut halves in a dry skillet over medium heat for 3–4 minutes, shaking the pan frequently, until fragrant and lightly browned. Remove and let cool slightly.

Caramelize walnuts (optional)

For candied walnuts (traditional), in a small saucepan combine 1 tablespoon honey and 1 tablespoon water over medium heat. Add the toasted walnuts and stir until the honey syrup thickens and coats the nuts, 1–2 minutes. Spread on parchment to cool and separate. Use the candied walnuts in place of plain toasted walnuts if you prefer a sweet crunch.

Make glaze

In a bowl, whisk together honey, sweetened condensed milk, mayonnaise, lemon juice, rice vinegar, salt, and cayenne (if using) until smooth and slightly thickened. Taste and adjust balance — add a little more lemon if too sweet or 1/2 teaspoon more mayonnaise to mellow. The sauce should be creamy, glossy, and cling to prawns.

Combine prawns and glaze

Place the fried prawns in a clean bowl. Pour the glaze over the prawns and gently toss with tongs or two spoons to evenly coat each prawn. Work quickly so the coating clings; do not over-stir or prawns may lose crispness. If using candied walnuts, roughly chop them and add to the bowl; otherwise fold in the toasted walnut halves.

Finish & Serve

Transfer glazed prawns to a serving plate. Sprinkle toasted sesame seeds and sliced green onions over the top. Arrange lemon wedges on the side for optional brightening. Serve immediately so prawns remain crisp.