Preheat the oven to 350°F and line 2 baking sheets with parchment paper or spray with non-stick spray.. (To get best results, use parchment paper)
In a medium bowl, sift the flour, baking soda and salt together.
In another large bowl, using an electric mixer at medium speed, beat together the butter, and sugars until smooth and mixed together well.
Add the egg and vanilla and mix on low speed until mixed in.
Gradually add the flour mixture and mix in until just incorporated. Do not keep mixing - do not overmix.
Add Reese's Pieces, white chocolate and butterscotch chips and stir with a wooden spoon, again no overmixing, just until incorporated.
Chill dough if dough is warm for 10-15 minutes.
Using a small or large ice cream scoop or heaping tablespoon, drop the dough onto the prepared baking sheets, 6 to 8 per pan, depending on size you are making.
Bake the cookies, 1 sheet at a time, until the bottoms and edges are lightly browned and the tops feel firm when lightly touched,
Small cookies bake 8-10 minutes
Large cookies bake 10-13 minutes. Extra large cookies, 15 minutes.
Let the cookies cool for 5 minutes on the baking sheets, then transfer the cookies to wire racks to cool completely.
Makes 12 -30 cookies depending on size.