Preheat your oven to 350°F (175°C).
Cream together the softened butter, granulated sugar, and light brown sugar until light and fluffy (about 2-3 minutes).
Add the eggs one at a time, mixing well after each addition. Then mix in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, cream of tartar, and kosher salt.
Gradually mix the dry ingredients into the wet mixture until just combined.
Fold in the butterscotch chips and English toffee bits until evenly distributed.
Scoop rounded balls of dough onto a baking sheet lined with parchment paper, leaving space between each.
Bake for 10-12 minutes, until edges are golden and centers are slightly underbaked.
Allow to cool on the baking sheet for 5 minutes before transferring to a cooling rack.
