Melt 2 tablespoons of butter in a small sauce pot, over a medium-low heat. Add in the 1/4 cup of cream. Mix to combine.
Add in the 1/2 cup brown sugar, mixing until all of the sugar has dissolved within the liquid. Increase heat to medium, bringing mixture to a low simmer.
Let the mixture simmer for about 5 minutes. Do not stir it at this point. You can swirl it around, within the pot, but if you stir it, the caramel sauce will end up grainy. Also, don't let it boil, so reduce the heat if need be. You don't want to burn the sauce.
Turn off the heat, add in the 2 tablespoons of vanilla extract and soy sauce, plus a pinch of salt. Swirl to combine.