Preheat the oven to 350 degrees F and generously grease and flour (4) 8-ounce wide-mouth jelly jars.

Place the dates in a small pot, along with the rum.  

Heat over medium high heat until boiling, then reduce the heat and simmer for 5 minutes or until the dates are softened.  

Remove from heat and stir in the baking soda.  

Transfer the mixture to a food processor or mini chopper and process until smooth.

Cream the butter and brown sugar in a large mixing bowl.  

Add the egg, ginger, and vanilla, and mix until combined.  

Scrape the bottom and sides of the bowl with a silicone spatula, then stir in the reserved date mixture, flour, baking powder, and salt.  

Divide the mixture equally between the prepared jars, and bake for 35 minutes, or until a cake tester comes out clean or with a few moist crumbs.

Cool slightly and top with warm Butter Rum Sauce.

Place the sugar and water in a small pot and cook over medium-high heat, occasionally swirling the pan, until it turns a deep amber color.  

Reduce the heat to low and whisk in the cream.  

Stir in the butter and salt, and remove from the heat.  

Add the dark rum and transfer the mixture to a heat safe vessel to cool for about 15 minutes before serving.