Wash the rhubarb and trim as little off the ends as possible. In a small saucepan, heat rhubarb, ¼ cup sugar, and 4 tablespoons water over medium heat. Cook until the rhubarb falls apart, adding water by the tablespoon if the rhubarb sticks to the bottom of the pan. At this point, either use an immersion blender to puree the mixture, or (if you’re like me and your blender is otherwise occupied) push the mixture through a strainer—the first method is definitely easier.

Put a couple inches of water into the pot of a double boiler and set it over medium heat. Put the egg yolks, the remaining ⅓ cup plus ⅛ cup sugar, the butter, lemon zest, and lemon juice in the bowl of the double boiler and whisk to combine. When the sugar has dissolved completely, mix in the warm rhubarb puree by the spoonful, to temper the eggs. When all the rhubarb has been mixed in, set the bowl over the pot; the water should be simmering. Stir for about 5 minutes, until warm and slightly thickened. Remove from the heat. Press through a fine-mesh strainer—this will give your curd that smooth, pudding-like texture—into a jar or other container with lid. Once cooled, the curd will keep in the fridge for up to a week.