To prep the rhubarb stalks wash them well and then top and tail each stalk by removing any white root and where the stalk branches into leaves. Then slice vertically into 1/2 inch strips and finally dice horizontally.
In a small saucepan on medium-high heat combine rhubarb, sugar, and water. Bring to a boil and then reduce to medium low to simmer. Cook for about ten minutes until the rhubarb is soft and broken down.
Using a spatula to help, pass the rhubarb mixture through a sieve over a heat-safe bowl. The spatula will help by manually breaking down the rhubarb further. The liquids will separate. Let both the rhubarb solids and the liquids cool. Add the rhubarb solids back into the saucepan.
Add three eggs to a separate bowl and whisk until uniform. Pour the rhubarb liquids into the egg and whisk until well combined.
Pop the saucepan back on the stove on medium heat, and slowly pour in the egg mixture, whisking constantly for about ten minutes. The curd will start to thicken and stick to the whisk instead of dripping off like a liquid would.
If you are adding pitaya powder or food coloring, add it now.
Pass the mixture back through the sieve to catch any accidentally cooked egg bits. While still warm, stir in the butter until completely melted.
Pour into a jar and let cool. This can be stored in an airtight container in the fridge for up to one week.