Preheat your oven to 200°F (100°C). Simultaneously, heat a large pot of oil for deep frying.
Melt butter in a large saute pan. Add the walnuts and cook until the butter starts to brown. Mix in sugar, water, and honey, then reduce until you achieve a sticky consistency that coats the walnuts.
Spread out the walnuts on a baking tray lined with baking paper, ensuring they aren’t touching. Bake for 10 minutes.
While the walnuts are baking, prepare the honey mayo sauce. In a bowl, combine mayo, condensed milk, honey, and lemon juice. Set aside.
In another mixing bowl, whisk together the egg and water. Gradually mix in cornflour, one tablespoon at a time, until you have a thin batter.
Season the shrimp with salt and pepper, then stir them into the batter until they're fully coated.
Deep fry the shrimp in the preheated oil for 2-3 minutes. Do this in batches, if necessary, to avoid overcrowding the pot. Once fried, use a slotted or fryer spoon to transfer the shrimp to a wire rack to drain.
Place the fried shrimp into a large mixing bowl, then toss them with the prepared honey mayo sauce until they're well-coated.
Serve the shrimp topped with the candied walnuts and a sprinkle of sliced scallions. Enjoy this savory-sweet, crunchy delight!