There are likely many other recipes for hot fudge sauce that have fewer ingredients or take less time to make, but I'm sticking with this one. It's from my mom (major points right there) and the simmering time on the stove makes you feel "like you're in a chocolate sauna" (to quote my sister-in-law, Gwen).
Hot Fudge Sauce Recipe
1 cup sugar
1/4 cup unsweetened cocoa powder (Scharffen Berger or Valhrona are especially amazing)
2/3 cup milk
1/2 cup light corn syrup
2 squares (2 oz.) unsweetened chocolate, chopped
1/2 stick (4 Tablespoons) unsalted butter
2/3 cup heavy cream
2 teaspoons vanilla extract
1. Sift sugar & cocoa into a heavy medium-sized saucepan. Stir well.
2. Stir in milk and corn syrup. Bring to a boil over medium heat, stirring constantly. Boil/simmer for ten minutes, stirring occasionally.
3. Remove from heat and stir in unsweetened chocolate and butter, until melted. Gradually stir in cream.
4. Return to a boil over medium heat, stirring constantly. Boil for three minutes, stirring occasionally.
5. Remove from heat. Stir in vanilla extract. Cool.