Line an 8" x 8" pan with parchment paper and spray with cooking spray.
Combine butterscotch chips, condensed milk, and salt in a microwave-safe bowl. Microwave on high for 50 seconds, stir, then microwave for 15 seconds until melted. Add vanilla and stir.
Pour the mixture into the prepared pan and refrigerate for 2 hours until firm.
Remove from pan, peel parchment, and cut into pieces.
Notes
Store in an airtight container in the refrigerator for best results.