Ensure the skin of the duck is dry and score in a 6-10mm (¼-½") crosshatch pattern with a sharp knife, ensuring you do not pass through to the flesh.
Season with the salt and place skin side down in a cold 28cm or 11" frying pan or skillet, turn the heat to low-medium and allow to cook for 8-12 minutes or until golden brown.
Slit the red chillies in half lengthways.
As soon as the duck breasts have given off enough oil, add the slit chillies to the oil.
Cut the shallot in half, peel it and then dice it as finely as you can.
Roughly tear the lime leaves into pieces, making sure you remove the central vein.
Cut the pineapple into 2-3cm (¾-1¼") pieces.
When the duck is nicely golden, remove it from the pan and set it aside, skin side up.
Drain the pan of all but about a tablespoon of duck fat and return it to a medium heat. Add the shallots, garlic and ginger paste and cook for 1 minute.
Add the Thai curry paste and cook for two minutes, stirring and mashing all of the time.
Pour in the coconut milk and add the lime leaves, lemongrass paste, brown sugar, lime juice and fish sauce, then stir to combine and bring to a simmer.
Add the duck breasts, skin side up and cook until the desired level of cooking. I aim to remove at around 53-54°C or 127°F.
Remove the duck and allow it to rest covered with foil for 5 minutes.
Add the pineapple to the sauce and have a taste before refining the levels of sugar, lime juice and fish sauce to your taste.
Shred the Thai basil and stir it through the sauce just before serving.