1. Place the cream, brown sugar and vanilla into a saucepan and bring to a simmer, whisking to ensure the sugar dissolves.
2. Remove from the heat, add the marshmallows and whisk to combine.
3. Pour over the dark chocolate and whisk until the chocolate has completely melted and incorporated.

Notes:

• If not using immediately, cover the fudge sauce with plastic wrap and store at room temperature for up to 3 days.
• Prior to using, microwave for 30 seconds and whisk to combine.