My grandmother Vesta, a dedicated military wife, would make these for her eight children along with all of her other homemade delights. I will never forget opening college care packages filled with bars for my roommate and me. These were huge hugs from home.
In a medium bowl, whisk the milk and vanilla into the powdered sugar, then whisk in the melted butter, to form a glaze. Cover and set aside until ready to coat the cookies.
Heat the oven to 350 degrees. Grease a13-by-9-inch baking pan. Line the bottom of the pan with parchment, and grease the parchment.
In a medium bowl, whisk together the flour, baking powder and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, cream together the butter and sugar until light and fluffy, 3 to 5 minutes. Slowly beat in the flour mixture until fully combined, then stir in the chocolate chips.
Press the dough into the prepared pan and bake until the cookie just begins to brown, 20 to 25 minutes (the cookie should be soft even as it cools). Rotate the pan halfway through for even baking.
While the cookie is still warm, pour the glaze over and tilt the pan so the glaze spreads evenly. Cut the cookie while warm into bars.