Combine mince, cheese, shallot, pickle, Henderson's, mustard, and ketchup in a bowl.
Place a heaped ½ tablespoon of filling in the center of a dumpling wrapper. Moisten edges with water, fold, and pleat to seal in the filling (if necessary, you can find detailed tutorials on dumpling-folding via your favourite search engine). Gently press the rounded bottom of the dumpling against your cutting board or counter so it sits upright. Repeat until all the filling is used.If you plan to freeze the dumplings, place them on a tray (either lined with nonstick paper or dusted with flour) that fits in your freezer, ensuring they're not touching. Slide the tray in and leave for an hour or two, until the dumplings are solid enough, and then you can transfer them to a freezer bag. Heat oil in a nonstick pan over medium high heat. Add 6 dumplings (you can add more; just don't let them touch) flat side down, and fry until bottoms are golden brown (1-2 minutes).
Carefully pour in â…“ cup (80 millilitres) water, cover immediately and steam for 4-6 minutes, until the water evaporates. Cooking times may vary depending on your hob, but a clear lid is useful so you can easily see what's going on.
Remove the lid and continue cooking for another 2 minutes or so, until the dumplings have a golden crust on the bottom.
Serve with Shanxi vinegar or your favourite condiment. Or eat as is. I'm not the boss of you.