3. In a large bowl with a hand mixer or stand mixer with paddle attachment, combine dry ingredients. Add butter, egg and vanilla and mix until a soft dough forms.
4. Mix in all of the chocolate chips with a rubber spatula.
5. Transfer dough to the prepared baking pan and spread it evenly around the square baking pan.6. Bake for 20-25 minutes until golden brown around the edges or until a toothpick inserted comes out clean.