Combine evaporated milk, brown sugar, corn syrup, and salt in a saucepan over medium heat.
Bring mixture to a boil and cook until just reaches the soft ball stage. This is 230 degrees on a candy thermometer.
Remove from heat, add butter and cool until about 200 degrees.
Add walnuts and stir.
Beat fudge until it has just lost its shiny gloss.
Immediately pour into a prepared pan lined with wax paper. Use a loaf pan if you want thicker fudge. Cool completely.
Cut into 24 pieces.
Store in an airtight container.
Watch your fudge carefully at all times. To be successful you must pay attention to it while it is cooking and while you are beating it. If you do overbeat it, add a little bit of milk to the mixture to try and loosen it up some.