Start by making the sauce. Whisk together the egg yolk, salt, pepper and vinegar, then very gradually whisk in the grapeseed oil. Start with just a few drops to create an emulsion, then increase the amount of oil, whisking all the while. Once all the oil has been added and your sauce is nice and thick, stir through the chilli garlic sauce.
Whisk all the batter ingredients together and combine well.
Heat around 5 inches of vegetable oil in a pan suitable for deep frying until it reaches 180°C or 355°F. Working in batches of 2-3 small handfuls, coat the shrimp in the tempura batter and gently drop into the hot oil, frying for a few minutes until golden. Remove the shrimp from the oil and place onto a paper towel-covered tray to drain. Repeat the process until all the shrimp is cooked.
Transfer the fried shrimp to a large bowl, pour over the sauce and toss to coat. Finish with a splash of yuzu or lemon juice and garnish with chopped chives.