Pre-heat the oven to 220 degrees. Line a baking sheet with greaseproof paper.
Drain the mushrooms and finely chop.
Heat the olive oil and sesame oil in a wok over a high heat. Add the onions, garlic, ginger and chilli and stir-fry for 2 minutes. Add the leeks and carrot and continue to stir fry for a further 2 minutes. Finally, add the mushrooms and stir-fry for 1 minutes. Remove from the heat and season with the soy sauce.
Working quickly, brush the sheets of filo pastry with a little melted butter on a flat work surface. Place tablespoons of the vegetable filling in the lower centre of the filo pastry as you look at it. Fold the edges in and over the filling and then roll up into a cigar shape, tucking the pastry around the filling tightly to secure.
Arrange on the baking sheet and bake for 15-20 minutes, turning halfway through, until golden brown and crispy.
Remove and arrange on a serving plate and sprinkle the Maldon salt on top of the spring rolls. Garnish with a sprig of coriander and serve immediately.
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