Combine cranberries, sugar, water, orange zest, orange juice, and salt in a medium saucepan. Bring to a boil over medium-high heat, stirring occasionally. Once boiling, reduce heat to medium and simmer for 10-12 minutes, stirring occasionally, until all the cranberries have burst and the mixture looks soupy and deep red.

Set a fine-mesh sieve over a large bowl. Working in batches, pour the hot cranberry mixture into the sieve. Use a spatula to press and scrape the solids, extracting as much smooth pulp as possible. This takes 3-4 minutes of active pressing. Discard the seeds and skin left behind. You should have about 2 cups of smooth cranberry liquid.

Lightly oil a 1-pint mold or clean 15oz can with neutral oil, then line with plastic wrap, leaving overhang on all sides for easy removal. If using a proper mold, you can skip the plastic and just oil it well.

Pour the warm, strained cranberry liquid into the prepared mold. Let cool to room temperature, about 30 minutes, then cover and refrigerate for at least 6 hours or overnight until completely firm.

To serve, invert the mold onto a serving plate. If it doesn't release immediately, dip the bottom of the mold in warm water for 10 seconds, then try again. Remove plastic wrap if used. Slice with a sharp knife dipped in hot water for clean cuts.