Step 1: Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or a silicone baking mat.
Step 2: In a large bowl, cream together the softened unsalted butter, light brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
Step 3: Beat in the large egg and vanilla extract until well combined, scraping down the sides of the bowl as needed.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
Step 6: Gently fold in the butterscotch chips and white chocolate chips (if using) until evenly distributed throughout the dough.
Step 7: Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Step 8: Bake for 10-12 minutes, or until the edges are lightly golden and the centers are still slightly soft. They will continue to set as they cool.
Step 9: Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.