Put all the ingredients into the blender, minus the bourbon. Blend until smooth.
Put a medium sized pot on the stove on medium heat and add the mixture. Bring to a boil and reduce the heat to low after that. You need to be whisking the whole time so lumps don't form. Cook the mixture for about 10 minutes. Take off the burner and let it cool.
After it cools down, blend it again and pour through a strainer. Add in the bourbon (which is optional, of course!)