For the paste:
Put the coriander,cumin and peppercorns in a heavy based pan and set over a medium heat. Stir the spices until they emit a roasted aroma and turn lightly golden. Cool and grind in a spice grinder or mortar and pestle until fine.
Put all the remaining ingredients in a food processor with the spices and blend until you have a smooth paste.
For the curry:
Trim the meat of any excess fat and sinew and cut into 5cm cubes.
Heat the oil in a heavy-based pot and fry the onions until brown.
Add the meat,season with salt and continue to cook until browned all over.
Open the can of coconut milk and scoop out the thick cream that has risen to the top. Add this and the paste to the pot,lower the heat and cook gently for about 5 minutes. Add the water,the remaining coconut milk,the cinnamon and bay leaves and cook,covered on a steady simmer for 1 hour.
Add the potatoes and continue to cook for another 30 minutes or until the meat and potatoes are tender. You may need to add a little water to the curry as it is cooking. Season to taste with a little fish sauce,palm sugar and tamarind paste or lemon juice.
To serve:
Garnish with roasted,crushed peanuts,sliced spring onions and coriander sprigs. Serve with steamed basmati or jasmine rice.