01 -
Preheat oven to 175°C and line two baking sheets with parchment paper.
02 -
In a large bowl, beat the butter, brown sugar, and granulated sugar with an electric mixer at medium speed until smooth and no butter chunks remain.
03 -
Incorporate the egg and vanilla extract on low speed until fully combined.
04 -
Add the flour, baking soda, and salt to the bowl. Mix on low just until incorporated. Do not overmix.
05 -
Fold in the butterscotch chips, semisweet chocolate chips, and optional chopped walnuts, mixing only until evenly distributed.
06 -
Scoop dough using a heaping tablespoon or ice cream scoop onto prepared sheets, spacing 6 to 8 per tray depending on size. Gently press additional chips on top if desired.
07 -
Bake one sheet at a time in the centre of the oven until edges and bottoms are lightly browned, and tops are set. For medium cookies, bake 8-10 minutes. For large cookies, bake 10-13 minutes.
08 -
Let cookies cool for 5 minutes on the baking sheets, then transfer to wire racks to cool completely. Sprinkle sea salt flakes on top while still slightly warm.