Place the chopped rhubarb and water in a medium saucepan over medium heat. Cover and simmer for 10-12 minutes until the rhubarb is completely soft and broken down.

Transfer the cooked rhubarb to a blender or food processor and pulse until smooth. Pass the puree through a fine-mesh sieve into a bowl to remove any stringy fibers, pressing down to extract all the juice.

In a clean heavy-bottomed saucepan, whisk together the rhubarb puree, sugar, lemon juice, salt, and egg yolks until well combined.

Cook the mixture over low heat, whisking constantly to prevent the eggs from scrambling. Continue cooking for about 8-10 minutes until the mixture thickens and coats the back of a spoon.

Remove the pan from the heat. Add the cubed butter one piece at a time, whisking continuously until each piece is fully melted and the curd is glossy and smooth.

Pour the curd into clean glass jars. Place a piece of plastic wrap directly on the surface of the curd to prevent a skin from forming, then let it cool to room temperature.

Refrigerate for at least 4 hours or overnight to allow the curd to fully set before serving.