Line a 9-by-13-inch pan with foil and coat it with nonstick cooking spray.
Combine condensed milk, vanilla extract, and salt in a bowl. Add confectioners’ sugar a little at a time and stir with a wooden spoon until fully incorporated. Add coconut and stir until combined.
Pour the mixture into the baking pan and press it into an even layer. Chill in refrigerator until firm, about 1 hour.
Using a sharp chef’s knife, cut the candy into small rectangles.
Set up a parchment-lined sheet tray. Melt the milk chocolate and butter in a bowl over a double boiler until almost fully melted, stir to combine. Ensure the mixture is smooth and there are no chunks of chocolate left. Dip each rectangle into the melted chocolate, covering completely, and place gently on the prepared sheet tray to set. Repeat this process until all rectangles are dipped. Refrigerate for 30 minutes or until chocolate has set. Store in the refrigerator until ready to serve.