Lightly coat an 8x8 square pan with cooking spray, then line with plastic wrap smoothing out as much as possible.
In a heavy bottom sauce pan, add evaporated milk, brown sugar, butter, and salt. Bring to a boil, stirring continuously over medium-high heat.
Once mixture comes to a boil, reduce head to medium-low and clip candy thermometer on the side of the pan. Cook until temperature reaches 235°F, stirring occasionally.
Once mixture reaches 235°F, remove from heat and transfer to a heat proof bowl or standing mixer. Using paddle attachment or hand mixer, add confectioners sugar stopping to scrape down the sides of the bowl if needed. Once incorporated, beat on medium speed for four minutes. Reduce speed to low and add vanilla. On low speed add walnuts and mix until evenly incorporated, less than 1 minute.
Transfer to the prepared 8x8 pan, scraping the side of the mixing bowl with a rubber spatula. Store pan in the refrigerator for 25-30 minutes until the middle of the fudge is set. Once set, use plastic wrap to easily remove from the pan. Remove plastic wrap and transfer to a cutting board. Cut square into 6x6 rows.