Combine the evaporated milk, brown sugar, butter, and salt in a heavy-bottomed medium saucepan. Place over medium heat and bring to a boil, stirring until smooth. Continue to simmer, stirring frequently, until a candy thermometer reaches 238°F (see Notes).
Remove from heat and pour into a heat-proof bowl. Add the vanilla and combine with a hand-held mixer. Add the powdered sugar in small additions while continuing to beat with the mixer. Mix until smooth. Add the walnuts and mix until just combined.
Spread the fudge into an ungreased 8-inch square pan (line with parchment or wax paper if you like). Let cool completely, about 1 hour, or chill in the fridge for 30 minutes. Slice with a sharp knife. Store fudge in an air-tight container for several days.
Notes
Notes
Temperature will need to be adjusted if you live at high altitude. Decrease temperature by 2°F for every 1,000ft of elevation. I live in Utah at over 4,000ft and cooked my sugar to 230°F.
If you do not have a hand-held mixer, you can also use a stand mixer fitted with a paddle attachment. I'm sure you can also mix by hand with a little bit of elbow grease.
To toast walnuts, spread in a single layer on a sheet pan and set under the broiler for 1-3 minutes, stirring at least once. Keep a very close eye on the walnuts so they don't burn, and pull them from the oven when they are fragrant and start to turn lightly brown.