I found this today - definitely making it this week.
1/4 cup granulated sugar
1/3 cup brown sugar
1 tsp. vanilla
1 1/4 cup flour
1/2 tsp. salt
1/2 tsp. cream of tartar
1/2 tsp. baking soda
1 (heaping) cup butterscotch chips
In a small bowl, whisk together the flour, salt, cream of tartar and baking soda.
In the bowl of a stand mixer, cream the butter and sugars together until combined and creamy. Add the egg and vanilla and mix for several minutes until light, fluffy and a pale yellow color.
With the mixer on low speed, add the dry ingredients and mix until fully combined. Add in the butterscotch chips.
Turn the dough out into the prepared pan and use an offset spatula to spread into an even layer. Bake in the preheated oven for 20-22 minutes, until the edges are lightly brown and set. Remove from the oven and cool in the pan on a wire rack.
Add in some chocolate chips, white chips, peanut butter chips or caramel bits in place of some of the butterscotch – or make a combination of your favorites!