Melt the butter in a medium-sized heavy-bottom saucepan over medium.
Add the sugar and whisk to combine.
Stir in the salt.
Increase the heat to medium/high and, using a candy thermometer, continue to cook and stir gently, yet very frequently, until the mixture until the toffee reaches the hard-crack temperature on the candy thermometer of 300-degrees Fahrenheit. *Note - this can take up to 10 minutes or more. Do NOT walk away from the stovetop.
**Special Note - NEVER heat the toffee over high heat as this will cause the candy mixture to break and separate. See notes below for high-altitude instructions.
Meanwhile, line a baking sheet with parchment paper and spray it liberally with baking spray. Set aside.
Once the toffee has reached the hard-crack temperature, remove the pot from the heat and stir in the vanilla extract, and the cashews until evenly coated.
Spread the butter toffee cashews in an even layer onto the prepared baking sheet and cool completely.
Once cooled, break the candy into bite-sized pieces. Set aside.
Melt the chocolate chips in a microwave-safe bowl (on medium/low power) and stir frequently, until smooth and creamy.
Drizzle the melted chocolate over the butter toffee cashew crunch candy and allow the candy to set until firm. Do NOT refrigerate.
Store in an airtight container in a cool location.