In a 1-quart stainless steel saucepan, combine cream, water, corn syrup, brown sugar, cocoa powder and salt over medium-low heat. Whisk frequently until sugar is dissolved.

Remove from heat and add the chopped chocolate. Let it melt gently for 1 minute, then return to medium-low heat.

Once it simmers, increase heat to medium and let boil gently for 3-5 minutes while whisking constantly. Do not boil vigorously.

For thinner sauce, boil 3 mins; for thicker, cook 5 mins. It should be smooth and glossy. Stir constantly to prevent burning.

Remove pan from heat and stir in vanilla extract. Let cool for 15 minutes before serving warm or pouring into a jar.

Store cooled sauce in a sealed jar in the refrigerator for up to 3 weeks. Reheat very gently before serving.