
Place the pineapple juice in a saucepan. Heat over medium or medium high heat and bring to a boil. Let the juice simmer for about 20 minutes or until the juice reduces in half to make 1 cup of concentrated pineapple juice. Transfer the juice into a jug to make sure that you have 1 cup. If you have less than 1 cup, then you can top it up with a little pineapple juice. Set aside.
Place the sugar and cornstarch in a small dry bowl. Whisk to combine the cornstarch and sugar well. This step is especially crucial if you're using Instant ClearJel (to prevent lumps).
In the saucepan (I use a 5 qt pot), add the sugar-cornstarch mixture, egg yolks, and lemon/lime juice, and whisk until you have a smooth mixture. Make sure there are no cornstarch or egg yolk lumps.
Pour in the concentrated pineapple juice while stirring to form a smooth mix. Add the butter.
Heat the mixture over medium-high heat, while frequently whisking, until the mixture comes to a boil.
When the mixture comes to a boil, lower the heat and continue to cook the pineapple curd while continuously whisking to prevent the egg yolks from scrambling.
The pineapple will start to thicken more and more after it comes to a boil, and then continues to cook. Cook while whisking for a further 5 - 6 minutes (depending on the pot that you use), until the pineapple curd registers between 180 - 190°F / 82 - 88°C.
The pineapple curd might start to look a little translucent, and this is OK, as long as the eggs are not scrambling.
Optional but recommended - Remove the pot from the heat and use a stick blender to blend the pineapple curd. Alternatively, you can place the curd in a blender or food processor and blend for about 1 - 2 minutes. This will make the curd creamy.
Pass the pineapple curd through a sieve into a bowl to remove any lumps.
Cover the bowl with plastic wrap. Make sure the wrap is touching the whole surface of the curd to prevent a skin from forming on top. To speed up the chilling time, you can spread the curd in a large, shallow pan instead.
Alternatively, transfer the mixture into a glass storage jar with a tight-fitting lid.
Let the curd cool down a little before transferring it to the fridge and then let it completely chill (preferably overnight).
Serve the curd chilled.