Let the green onion, ginger and salt steep in the water for at least 15 minutes.

Strain, then refrigerate.

Combine all the filling ingredients except the pork and let them infuse for 10 minutes.

Add the pork and stir in one direction until the liquid is absorbed and the mixture becomes sticky.

With a fingertip, moisten the edges of a wrapper with a little water.

Place a small spoonful of filling in the centre.

Fold the wrapper in half to make a rectangle.

Press firmly to seal the edges.

With the folded edge facing you, wet one corner and overlap it with the opposite corner.

Press to seal (see video below).

Bring a large pot or wok of water to a rolling boil. Gently drop in the wontons, stirring so they don’t stick. Cook in batches if needed.

When the wontons float (about 6–7 minutes), boil for 1½ minutes more.

Place the chilies and Sichuan peppercorns on a microwave-safe plate and microwave on high until fragrant, about 15 seconds.

Transfer to a mortar or food processor and crush to the texture of red-pepper flakes.

Tip the crushed spices into a heat-proof bowl with the garlic and sesame seeds.

Heat the vegetable oil over medium heat until it shimmers, then carefully pour it over the spice mixture—it should sizzle.

Let stand for 5 minutes, then stir in the sesame oil.

In a small bowl, stir the sugar, vinegar and soy sauce until the sugar dissolves.

Whisk in the chili oil. Set aside until needed (the sauce keeps up to 2 weeks in the fridge).

Arrange the wontons in a shallow bowl and spoon the spicy sauce over the top.