In a medium saucepan, heat the cream and 1-2 cups of the cereal until it’s steaming; remove from the heat and let sit for half an hour or so to infuse the cream with the flavour of the cereal. Strain and return the cream to the pot; sprinkle the gelatin overtop and let sit for a few minutes to soften.
Turn on the heat and warm the infused cream, whisking until the brown sugar and gelatin are dissolved. Divide among ramekins or other small dishes, or Chinese soup spoons. Refrigerate for 3-4 hours, or until set.
To make the dust, put the Chex into a zip-lock bag and crush with the back of a spoon or rolling pin - you want some texture, not total dust. Sprinkle over the panna cotta just before serving.
Makes 6-8 panna cottas - or lots of spoons.