Preheat oven to 375 degrees F (190 degrees C). Butter a 9x13-inch baking pan.
Mix flour, salt, and baking soda together in a bowl.
Combine butter, brown sugar, white sugar, and vanilla extract in a separate bowl. Beat in eggs 1 at a time. Mix sugar mixture gradually into flour mixture. Spread 1/2 the dough evenly into the prepared pan.
Bake in the preheated oven until partially firm, about 10 minutes. Leave oven on.
Cover the partially baked dough with chocolate bars, breaking up as needed to fit. Drop remaining dough over the chocolate as evenly as possible.
Bake in the hot oven until golden brown, 10 to 15 minutes more. Let cool.