In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set aside. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a large mixing bowl, use an electric mixer to beat the softened butter, granulated sugar together until light and fluffy, about 2-3 minutes.
Add the eggs one at a time, beating well after each addition, then add the vanilla extract. Mix until fully combined.
Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined. Be careful not to overmix. Fold in the toffee bits until evenly distributed.
Scoop about 1.5 tablespoons of dough and roll into balls. Place them on the prepared baking sheets, leaving about 2 inches of space between each cookie.
Bake for 10-12 minutes, or until the edges are set but the centers still look soft.
