In a large mixing bowl, cream together butter, brown sugar, and sugar until the mixture is light and fluffy.
Add the eggs, one at a time, mixing until combined.
Stir in vanilla.
Add the dry ingredients and mix until just incorporated.
Fold in the butterscotch chips. Chill for 30 minutes.
Preheat oven to 350℉ and line baking sheets with a silicone mat or parchment paper.
Scoop about 1½ Tablespoons of dough (a medium cookie scoop) and place about 2 inches apart on lined cookie sheet.
Bake 9-11 minutes, or until the edges begin to brown. It's okay if the centers look slightly underbaked, that will help to keep the chewy and delicious. Cool on the pan for 5 minutes, then move to a wire rack to cool completely.
Notes
Store in an airtight container at room temperature for up to a week. For longer storage, freeze for up to 3 months. You can also freeze the dough to bake later if you would like.