Preheat oven to 170°Celsius.
In a large bowl, add the butter, cream cheese, peanut butter, granulated sugar, brown sugar, egg and vanilla essence.
Beat the ingredients until they turn smooth and creamy.
Sift in the flour, cornstarch, salt and baking powder. Mix until combined.
Add two thirds of the butterscotch chips into the dough and mix with a spatula until the chips are well distributed. Reserve the remaining chips to press into the cookies later.
Using a measuring spoon or an ice cream scoop, scoop the cookie dough and shape lightly into balls.
Place the cookie dough balls on a parchment-lined baking tray. Press in the remaining butterscotch chips onto the cookies.
Chill the shaped cookie balls for about 45 minutes to 1 hour.
Bake the cookies in a preheated oven for 10 minutes, until the sides turn lightly brown.
Remove the tray from oven. Once the cookies have cooled down slightly, transferr them onto a wire rack to cool completely.