For the curry paste, in a mortar and pestle or spice grinder, grind the peppercorns and seeds together, then add the salt. Put this into a small blender (or keep pounding) and add the other ingredients one at a time. Blitz or pound until you have a smooth paste. (Leftover paste will keep in an airtight container in the fridge for a few weeks, or you can freeze it.) Set aside.
For the balls, place all the ingredients in a food processor and blitz until a paste forms. With wet hands, shape the mixture into walnut-sized balls. Put in the fridge while you make the curry sauce.
For the curry sauce, heat the oil in a large frying pan over medium heat. Stir in 2 tablespoons of the curry paste and cook until it becomes fragrant, about 1 minute. Add the coconut milk, stock, fish sauce and palm sugar or panela and simmer until reduced and thickened a little. Gently place the balls in the pan and cook in the sauce. This should take about 5 minutes. You may need to turn them depending on the depth and width of your pan
To serve, garnish with the coriander leaves and chilli and serve at the table in the pan.