Grease a 9×5-inch loaf pan with non-stick spray and line with parchment paper.
Whisk butter and brown sugar over medium-low heat until melted, about 2-3 minutes.
Add evaporated milk and bring the mixture to a boil. Let it cool for 30 minutes.
Mix in vanilla extract and salt, then beat in powdered sugar until smooth.
Fold in chopped nuts and transfer the mixture to the prepared loaf pan.
Refrigerate for 20 to 25 minutes until set, then slice and serve.