Combine granulated sugar and orange zest in a medium saucepan, massaging the zest into the sugar.

Whisk in egg yolks, blending until smooth, and then add orange juice and salt.

Cook over medium-low heat, stirring constantly until the mixture thickens, about 20-25 minutes.

Remove from heat and whisk in cold cubed butter until melted and creamy.

Strain the curd through a fine mesh sieve into a medium bowl to ensure smoothness.

Cover with plastic wrap directly on the surface and cool at room temperature for 30 minutes.