Set base of double boiler, filled with the appropriate amount of water, on stove on medium heat to bring to a simmer.
Zest your orange and add to double boiler insert (don't place it over the boiling water yet!)
Add eggs, orange juice, Allulose and vanilla bean paste (or bean and scrapings) to double boiler insert.
Whisk gently to incorporate.
Place double boiler over the simmering water in the pan.
Whisk constantly until the mixture takes on the consistency of Hollandaise sauce and coats the back of a spoon. This should take about 10 minutes, but if it isn't thickening, increase the heat a bit and keep whisking.
Once desired consistency is reached, remove immediately from heat and pour through mesh strainer to remove the zest, clumps and vanilla bean pod (if you didn't use the paste).
Whisk in butter one chunk at a time until incorporated.
Pour into jar or other airtight container.
Place plastic wrap directly over the surface of the curd to prevent a skin from forming.
Chill in refrigerater until completely cool before using.
Enjoy!