Separate your eggs and save your whites for another recipe. Add pineapple juice, lemon juice, and egg yolks to your saucepan and whisk well, ensuring that the egg yolks are thoroughly incorporated. Turn the stove to medium heat.
In a small bowl, stir together the cold water and cornstarch with a fork, then add that to the sauce. Whisk constantly to ensure nothing burns and that the sauce remains a uniform viscosity.
2 tablespoons cold water, 1 tablespoon cornstarch
Once the mixture boils, remove from the heat while continuing to whisk. Whisk for another several minutes until the mixture thickens to the point of leaving trails in the curd as you whisk.
At that point, add the butter and continue whisking until the butter is melted and thoroughly incorporated into the pineapple curd.
4 tablespoons butter
Pour your curd into a large liquid measuring cup and then use that spout to pour the pineapple curd into jars. Seal jars as you fill them, and store in the fridge for at least six hours before using to allow them to set and thicken properly. You can store them tightly sealed in the fridge for two to three weeks.