Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

In a large mixing bowl, combine cold unsalted butter, brown sugar, and granulated sugar. Beat until creamy and smooth, about 2-3 minutes.

Add in one large egg and a teaspoon of vanilla extract to the buttery mixture, mixing until well incorporated.

Gradually sift in all-purpose flour, baking soda, and salt. Mix on low speed just until combined.

Fold in butterscotch and semisweet chocolate chips evenly into the dough.

Using a cookie scoop or tablespoon, portion out the dough onto lined baking sheets, spacing them about two inches apart.

Optionally, press extra chocolate and butterscotch chips into the tops of the dough mounds.

Bake in preheated oven for 10-13 minutes, until edges are lightly golden and centers are set but still soft.

Let cookies cool on baking sheets for about 5 minutes and sprinkle with sea salt before transferring to a wire rack.