In a saucepan, combine the chopped rhubarb and sugar. Cook over medium heat until the rhubarb is soft and has released its juices, about 10 minutes.

Remove from heat and strain the mixture through a fine mesh strainer into a mixing bowl, pressing to extract as much liquid as possible.

Whisk in the eggs, lemon juice, and lemon zest until well combined.

Return the mixture to the saucepan and cook over low heat, stirring constantly until thickened, about 10 minutes.

Remove from heat and stir in the butter until melted and smooth.

Transfer the curd to a jar and let it cool to room temperature before refrigerating.