Add condensed milk, butter and brown sugar to a saucepan. Stir on low heat until melted.
Turn the heat to med/high and stir until it bubbles & thickens.
Turn off the heat, add the white chocolate & salt, and stir until combined.
Pour the mix into a lined 8x8" tin, smooth it out & sprinkle salt on the top. Refrigerate for 2 hours minimum.
