Preheat your oven to 350°F (175°C) to ensure even baking.
Line a baking sheet with parchment paper to prevent sticking.
In a large mixing bowl, combine melted butter, brown sugar, and vanilla extract. Mix until smooth and creamy. Add the egg and mix until incorporated.
Sprinkle in the instant butterscotch pudding mix and mix until fully integrated.
In a separate bowl, whisk together flour, baking soda, and salt. Gradually add to the wet ingredients, mixing just until combined.
Gently fold in 1 cup of butterscotch chips and chopped cashews.
Drop rounded balls of dough onto the prepared baking sheet, spacing them a couple of inches apart.
Bake for 10-12 minutes or until the edges are lightly golden.
Allow cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.