In a small saucepan, combine cranberry sauce, water, and orange zest over medium heat. Stir until smooth and warmed through.
In a separate bowl, whisk together the egg, egg yolk, sugar, and salt.
Slowly pour a small amount of the warm cranberry mixture into the egg mixture while whisking (to temper the eggs).
Gradually whisk the tempered egg mixture back into the saucepan with the rest of the cranberry mix.
Cook over medium-low heat, stirring constantly, until the curd thickens and coats the back of a spoon (about 5–8 minutes).
Strain the curd through a fine mesh sieve into a clean bowl to remove any solids.
While still warm, stir in the butter until fully melted and smooth.
Let cool slightly, then refrigerate until chilled and set.
When ready to serve the cheesecake, top generously with the curd and serve a little more on the side with each slice!