Preheat oven to 350 degrees and prepare cookie sheet with parchment paper or silicone mat.
Cream together butter and brown sugar for 2-3 minutes on medium speed. (Make sure your butter is not too soft. I prefer to use butter that is a little cooler than room temperature. If your butter is too soft the cookies will spread and be more flat.) Add eggs and vanilla. Increase speed of mixer to medium/high and blend for another 2 minutes.
Add flour, salt, and baking powder. Mix just until dry ingredients are combined. If you mix the dough too long after the flour has been added, you add extra air into the dough which will cause the cookies to rise and deflate and become crispy and hard.
Lastly add white chocolate and butterscotch chips. Gently fold the chips in to avoid over mixing.
Scoop cookies onto parchment or silpat lined cookie sheet. I like to use a medium cookie scoop (2 Tablespoons.) Bake for 10-12 minutes.
Let rest on the pan for about 3-5 minutes before placing on a cooling rack.