1. In a frying pan, heat 1 tbsp vegetable oil and fry onion, shrimps, mushroom, zucchini and corn until wilted.
2. Add butter and cook until melted. Then add all the flour and stir this mixture until combined well.
3. Pour the milk gradually and stir gently until the sauce has thickened.
4. Add all the ingredient A to season. Mix to combine evenly. Transfer the mixture into a container and place it in the refrigerator (or in the freezer if you are in a rush) until it has set.
5. Lay a spring roll wrap flat, tip down. Place the filling mixture centered in the lower tier of the wrap. Roll up tightly. Dab a little 'glue' mixture along the edges to seal. Repeat until you finish the filling mixture.
6. Pour enough oil in a wok or large saucepan and heat on medium-high until hot : Stick in a bamboo chopstick, if bubbles appear, it's hot enough :-). Place the rolls gently in the oil and cook both side, turning occasionally, until nicely and evenly golden. Transfer them to a plate lined with paper towels to drain the excess oil.
Repeat with the remaining spring rolls.
If you don't need to fry all for that day, then freeze the remaining rolls until you need them in a sealed freezer bag.