Heat the vegetable oil in a wok or saucepan over low-medium heat and add the garlic. Cook the garlic for about 3-4 minutes, stirring constantly, until it is lightly golden brown and then remove the garlic from the oil with a wire mesh sieve. Reserve both the fried garlic and the garlic oil.
Heat a large frying pan over medium-high heat. Dredge the salmon cutlets in the cornflour and add three tablespoons of the garlic oil to the pan. Season the salmon with salt and white pepper and fry for about three minutes on each side until just cooked through, then remove to a serving plate.
Heat a tablespoon of the garlic oil in the wok (reserve any leftover garlic oil for another purpose) and add the spring onions and black bean sauce. Toss for about a minute, until the spring onions start to soften, then add the chillies and celery leaves and toss for a further minute. Add the reserved fried garlic and turn off the heat, breaking up any clumps of garlic. Pour the mixture over the salmon cutlets and serve immediately.
