Sliced the rhubarb about 1/2-inch thick. Place it in a 4-quart sauce pan with 1/4 cup of sugar and let sit for 10 minutes. Add 1/4 cup water and stir together. On medium-high heat bring the mixture to a boil and then reduce to a low heat and cook until the rhubarb is tender, about 12 minutes. Stir occasionally to keep the rhubarb from sticking to the bottom of the pan. Don’t leave the rhubarb unattended or you risk burning it.
Place a medium coarse strainer over a bowl and scrape the rhubarb into the strainer. Use a large spoon to push the soft rhubarb through the strainer. You will have about 1 cup of rhubarb puree. Let the rhubarb puree cool to room temperature. At this point you can refrigerate the rhubarb puree up to 2 days. The rhubarb leftover in the strainer can be used in muffins, quick breads or stir it into your oatmeal.
Place the rhubarb puree in a clean nonreactive sauce pan. Add the lemon juice and the remaining 1/2 cup sugar. Whisk to combine and taste the mixture. At this point add more sugar, 1 tablespoon at a time if is not sweet enough. Add the egg yolks and whole eggs and whisk until well combined. Place the pan over medium heat and whisk continuously until the curd reaches 190 degrees. Do not let it boil, that could cause the eggs to curdle. Once the curd is at 190 degrees F remove the pan from the heat and whisk in the butter 1 tablespoon at a time.
Strain the curd, to remove the solids. Cover the surface of the curd with plastic wrap and refrigerate overnight. The curd will thicken as it cools. The curd is good is the refrigerator for up 1 week.