Hooray for National Hot Fudge Sundae Day!

What is the key to celebrating this most fabulous holiday? A damn fine hot fudge recipe. And with that, I am reposting the one I shared way back in January. After all, how does that old adage go? Oh yeah: If it ain't broke, don't fix it. This is the world's best hot fudge recipe.
Here's my idea of a great way to celebrate today:

First: 2 scoops of homemade Philadelphia-style vanilla ice cream (from David Lebovitz's incredible ice cream book!) drowning in this hot fudge, and topped with colored sprinkles, chopped nuts, and whipped cream.

Later: Gym or Wii Fit to remove some of the guilt.

Hot Fudge Sauce

2/3 c. heavy cream
1/2 c. light corn syrup
1/3 c. dark brown sugar, packed
1/4 c. unsweetened Dutch-process cocoa powder
1/4 tsp. salt
6 oz. fine-quality bittersweet chocolate (not unsweetened), finely chopped
2 Tbsp. unsalted butter
1 tsp. vanilla

Bring cream, corn syrup, sugar, cocoa, salt, and half of chocolate to a boil in a 1 to 1 1/2 quart heavy saucepan over moderate heat, stirring until chocolate is melted. Reduce heat and cook at a low boil, stirring occasionally, 5 minutes, then remove from heat. Add butter, vanilla, and remaining chocolate and stir until smooth. Cool sauce to warm before serving. Makes about 2 cups.

Cook's Note: Sauce can be made 1 week ahead and cooled completely, then chilled in an airtight container or jar. Reheat before using.