In a small saucepan, brown butter over medium heat. Whisk frequently and allow the butter to brown. Be careful not to burn. Remove from heat and pour and scrape browned butter and browned bits into a small bowl. Allow to cool down to room temperature before using.
Preheat oven to 325. Line baking sheets with parchment paper, set aside.
Toss flour, baking soda, baking powder and cornstarch together. Set aside.
Combine butter and sugars until smooth. Add in egg, egg yolk and vanilla and mix until completely incorporated. Stir in flour mixture until just combined. Fold in butterscotch chips and toffee bits until evenly distributed.
Roll dough into one rounded tablespoon balls and place one cookie sheet. Repeat the rolling process for the rest of the dough. If desired, stud the outside of dough balls with more butterscotch chips for a visual pop. Bake for 9-10 minutes. Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack to finish.
Cookies will stay fresh and soft for up to 3 days stored in an airtight container.