Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine melted butter and brown sugar. Whisk until smooth. Add egg and vanilla extract, whisking until fully incorporated.
In another bowl, whisk together flour and baking soda.
Gradually add the dry mixture to the wet ingredients, stirring with a spatula until just combined.
Fold in butterscotch chips and chopped chocolate gently.
Scoop rounded balls of dough onto a baking sheet lined with parchment paper, leaving 2 inches between each cookie. Bake for 10-12 minutes.
Allow cookies to cool on the baking sheet before transferring to a wire rack to cool completely.
