01 -
Preheat the oven to 350°F. Line 2 baking sheets with parchment paper.
02 -
In a large bowl, using an electric mixer at medium speed, beat together the butter, brown sugar, and granulated sugar until the mixture is smooth and free of butter chunks.
03 -
Add the large egg and vanilla extract to the sugar and butter mixture. Mix on low speed until combined.
04 -
Gradually add the flour, baking soda, and salt into the wet mixture. Mix just until the ingredients are incorporated—avoid overmixing.
05 -
Gently fold in the butterscotch chips, chocolate chips, and any optional walnuts. Mix only until incorporated.
06 -
Using a small or large ice cream scoop (or heaping tablespoon), drop portions of dough onto the prepared baking sheets, spaced about 6 to 8 per sheet, depending on cookie size.
07 -
Optionally, press additional butterscotch and chocolate chips into the tops of the cookies.
08 -
Bake one sheet at a time. Medium-sized cookies (2 tablespoons dough) bake for 8-10 minutes, while larger cookies (1/4 cup dough) bake for 10-13 minutes. Bake until edges are lightly browned and tops feel firm to touch.
09 -
Allow cookies to cool for 5 minutes on the baking sheets. Then transfer to wire racks to cool completely. Optionally sprinkle sea salt over the cookies while they cool.