Melt all the ingredients, except the essential oils if using, in a double boiler. You can make your own double boiler by placing a glass bowl over a medium-size saucepan.
Bring the water to a boil until all the ingredients are melted.
Remove the bowl from the heat and let cool slightly before adding in essential oils.
Stir well until well combined.
Pour the mixture into silicon molds or metal salve tins, whatever you prefer to use.
Let the mixture cool completely and then pop the bars out of the molds.
Store in an airtight container for up to one year.