Preheat oven to 350°F and grease a 9x13 inch baking dish
Beat butter and sugar until light, fluffy, and pale
Mix in eggs one at a time, then add vanilla and blend until smooth
Add baking soda and cream of tartar, then mix in flour just until combined, fold in chocolate chips
Whisk caramel sauce with flour until smooth
Press half of the dough into the pan, slightly up the sides
Pour caramel evenly over the dough layer
Drop remaining dough over the caramel layer
Bake for 25–35 minutes until golden and just set, cover edges if browning too fast
Cool completely before slicing to set the caramel