Add 2/3 cup of sugar into a saucepan. One quick thing to note! When making the orange curd, it's best to use a saucepan that's ceramic as opposed to metal. Some metal pans can give the curd a metallic taste.
Zest 2 large oranges into the saucepan and massage the zest into the sugar with your fingertips. This helps release the oil in the zest and gives this curd a bright, citrusy flavor.
Add in 6 egg yolks or 3 large eggs and whisk the mixture together until the ingredients are combined. Then mix in 1/2 cup of freshly squeezed orange juice and 1/2 tsp salt.
Cook on medium-low heat, stirring constantly with a rubber spatula or wooden spoon until the mixture thickens. This usually takes me 20-25 minutes (it can vary a lot based on the type and size of pan you use!). In the first 10-15 minutes, it won't seem like much is happening, but it'll start to thicken slowly after that, I promise! It should be thick enough to coat the back of a spoon once it's ready.
Remove the pan from heat, then add 1/2 cup of cold butter that's been cut into small pieces. Mix until the butter is fully melted, and the ingredients are combined.
Then pour the orange curd through a fine mesh strainer into a separate bowl to remove any bits of cooked egg, zest, or orange seeds. This gives it a perfectly smooth texture! Don't forget to scrape the bottom of the sieve to make sure you don't waste any of the orange curd.
Place the orange curd in the fridge to cool and thicken before using it. If you make this recipe in advance, cover it flush with plastic wrap to prevent it from forming a skin and store it in the fridge for up to two weeks.