Preheat the oven to 350 degrees. Line two baking sheets with parchment paper and set aside.
In a medium bowl, whisk the flour, baking powder, baking soda and salt together. Then set aside the flour mixture.
2 cups (250 g) all-purpose flour, spooned and leveled, ½ teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon salt
In a large bowl, cream the butter, brown sugar and granulated white sugar together with an electric mixer on high speed until light and fluffy, 2-3 minutes. (You can also add use the bowl of a stand mixer fit with a paddle attachment if you would rather.)
¾ cup (168 g) unsalted butter, softened, ¾ cup (165 g) light brown sugar, packed, ¼ cup (50 g) granulated white sugar
Add in the egg yolks and vanilla extract and mix on medium speed until pale in color and fluffy, 1-2 minutes. (Scrape the sides of the bowl as necessary.)
2 egg yolks, at room temperature, 1 tablespoon vanilla bean paste or vanilla extract
Add in the melted butterscotch chips and mix on medium speed just until combined.
¼ cup (50 g) butterscotch chips, melted
Add the dry ingredients to the wet ingredients and mix on low speed just until combined.
Mix the butterscotch chips and chocolate chips into the dough with a rubber spatula.
½ cup (100 g) butterscotch chips , ½ cup (100 g) semi sweet chocolate chips
Scoop the dough with a large, 2 tablespoon capacity cookie scoop. Arrange the cookie dough balls 3 inches apart on a parchment paper lined baking sheet. Bake for 10-11 minutes, until a light golden brown color.
After baking let the cookies cool on the cookie sheet for five minutes then transfer them to a wire rack to completely cool. While they're cooling, sprinkle extra chocolate chips, butterscotch chips and flaky sea salt on top of each cookie.
flaky sea salt for sprinkling on top, extra butterscotch and chocolate chips for sprinkling on top