How to Make It
In the bowl of a mixer, beat together butter, brown sugar, and granulated sugar until lightened and fluffy, about 3 minutes. Scrape down the sides of the bowl, and add corn syrup, eggs and vanilla. Beat on medium-high for 3 minutes. In a separate bowl, stir together flour, milk powder, salt, baking powder, and baking soda. Add to butter mixture and mix on low until just combined. Add butterscotch chips and stir to combine. Wrap in plastic wrap and refrigerate for at least 1 hour.
Preheat oven to 350°F. Line 2 baking sheets with parchment paper. Scoop balls of dough that are 1 3/4-inches in diameter and roll in hands until smooth. Place each dough ball on baking sheet 2 1/2 inches away from the others. Bake until edges have set, the bottom is lightly browned, and the top of the cookie is still soft, 15 to 17 minutes. Allow to cool slightly on the sheets before removing to a wire rack to cool completely.