In a food processor, purée the garlic and ginger and then add the prawns, water chestnuts, soy, spring onions, 1 teaspoon of the egg white and the coriander. Keep pulsing, leaving the mixture chunky, but together.
Lay out six of the wrappers, keeping the other wrappers covered with a tea towel so that they don’t dry out. Place a heaped teaspoon of the filling in each and brush the edges of the wrapper with the remaining egg white. Bring one side over, creating a triangle or half moon. Squeeze out any trapped air. Dab the corners with a little more egg white and cross over, then press them together to form a wonton. Continue until all the wrappers are filled.
To make the spicy Sichuan sauce, mix all the sauce ingredients together and pour into small bowls.
Bring a very large stockpot of water to the boil and have a cup of cold water ready. Add some of the wontons and then add the water. When it comes to the boil again, the wontons are ready to remove. It’s best to use a slotted spoon to scoop them out. Drain on a plate. Add the remaining wontons to the water, which should be boiling again. Repeat with the cold water and let cook.
Divide the wontons among the bowls of sauce, top with sesame seeds and chopped spring onions and serve immediately.