1. Mince your prawns with a sharp chef's knife, and put the minced prawns in a bowl.
2. If using shiitake mushrooms (recommended), soak in warm water until soft, about 15 minutes, then drain and gently squeeze out the water from each mushroom, and slice.
3. Soak your beanthread noodles in water for about 15 minutes, then, while still soaking, cut the beanthread into 1" length pieces using scissors (see picture). Drain, and put the cut beanthread into a bowl.
4. Make a flour paste by mixing 2 tablespoons all purpose flour with 1 tablespoon water. Keep aside. This will act like a glue to hold your wrappers together.
5. Open your package of frozen wrappers, remove from package, and set on a cooking sheet. Cover with a damp paper towel. As you remove each wrapper, keep the damp towel on top of your existing stack.