Preheat oven to 180C/350F/Gas 4.
Place half the potatoes in the centre of each sheet of foil, in one even layer.
Top each with half of the cheddar, bacon, chilli, and onion. Dot each with one tablespoon of butter.
Repeat with the other half of the ingredients on top.
Bring foil up around potatoes, sealing top and ends with double folds.
Cook for 45 minutes until potatoes are tender. Let packets stand for several minutes to cool slightly before serving.
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