In a blender, add the Atkin shakes, egg yolks, rum extract, cinnamon and salt. Blend on high until combined then pour into a medium sized sauce pan.
Pour in heavy cream and stir well. Heat over medium low heat.
Continue to stir over low heat for about 15-20 minutes until mixture thickens and temperature with a thermometer is 160 degree F.
Pour into a glass container, when slightly cooled try some and decide if you need to add any sweetener, stir well then place some plastic wrap right onto the mixture so a skin doesn't form while chilling in the refrigerator.