In a small saucepan, combine butter, brown sugar, and cream. Bring to a boil over medium-high heat; reduce heat, and simmer for 5 minutes. Remove from heat, and stir in salt and vanilla extract. Let cool completely, and refrigerate in an airtight container for up to 2 weeks. Rewarm before using.
Recipe by Victoria at https://victoriamag.com/ginger-cake-with-wine-poached-pears-recipe/