If you've only ever had spring rolls from a cheap Chinese restaurant or takeaway, these will be a revelation - they are crispy and fresh-tasting, and you'll actually want to eat them! You can make them with chicken or beef, or leave out the meat entirely for a vegetarian version.
For the Spring Rolls
Chop the pork into very small pieces. Fry in some of the sesame oil at high temperature for 2-3 minutes. Drain the meat and set aside.
Julienne the carrot and celery (juliennes are very fine sticks, about 2-3mm (one-eighth inch) square), finely chop the spring onions (but keep some of the tops for the dipping sauce and garnish) and shred the cabbage. Stir-fry the vegetables in sesame oil for 2 minutes, stir in the fish sauce and cook for another minute, then drain and set aside. You meat and veg should be quite dry, otherwise your spring rolls will be soggy.
For the Dipping Sauce
Mix the vinegar and soy sauce. Finely chop the ginger and chilli and add to the sauce. Set aside until needed.
Make the Spring Rolls
Mix 2 tsps flour with 2 tsps water - this will be the glue for your spring rolls. Take one sheet of spring roll pastry, and place it on your work surface at an angle of 45°. Spread 2 dessertspoons of filling in a horizontal band near the bottom corner of the pastry. Pick up the bottom corner and roll it over the filling. Roll it over one time, and then take the left corner of the pastry and fold it over the filling towards the centre. Do the same with the right-hand corner - you should now be looking at something that looks a bit like an envelope. Make sure the two edges are parallel to each other. Now roll the pastry a couple more times until you have a triangular flap left at the top. Spread glue on this, and then roll the spring roll over the flap. You've just made a spring roll!
Cook the Spring Rolls
Spring Rolls are normally fried in lots of oil in a wok. I guess it's possible to bake them, but I can't imagine that being very pleasant.
Heat several inches of vegetable oil in a wok or pan to a temperature of about 180°C (335°F). Carefully lower the rolls in the oil, and cook until golden - about 4-5 minutes. Remove from the oil and dry on kitchen paper.
Serve them with the dipping sauce in a small bowl and garnish with finely-chopped spring onion.