Hot Fudge
Source: rec.food.cooking/Nancy Wenlock

Here is a recipe irreverently ripped from the Back of the Box Gourmet book which I have tried with great success. The book, by the way, is very entertaining and has a few "classic" recipes like this one.
This is defintely the closest thing you'll find to THE drugstore soda fountain Hot Fudge! Enjoy!!

3/4 cup sugar
1/2 cup Hershey's cocoa
1/2 cup plus 2 Tbsp (5 ounce can) evaporated milk (I use a scant 1/2 cup - see note)
1/3 cup light corn syrup (I used a bit less)
1/3 cup unsalted butter (or margarine)
1 tsp vanilla extract

In medium saucepan, combine sugar and cocoa.
Then blend in evaporated milk and corn syrup.
Cook over medium heat, stirring constantly, until it boils.
Boil and stir for 1 minute.
Remove from heat and stir in butter and vanilla.
Serve warm.
Can be refrigerated and re-heated many times.

Note: You may have to play around a bit with the evaporated milk quantity - depends on where you are I guess. I am in a high altitude area.