Soak the mussels so that they release all of the sand.
Roughly chop the onions or shallots and grind them together with the garlic, the stock cube, the peppercorns and the dried chillies in a mortar or blender.
Heat an unfilled large saucepan and add the mussels. They open after approx. 2 - 3 minutes. Then add enough water to cover the mussels. Add the spice mixture and close with the lid.
After 1/2 hour simmer, carefully mix in the lemon juice, the salt and the whole scratched, fresh chilli pepper. Remove the pan from the heat and let it steep for another 5 minutes, then serve.