Pre heat oven to 325.
Lightly grease a 9×13 in. baking dish.
Whisk flour, cocoa powder, baking powder, baking soda,and salt in bowl.
On stovetop in saucepan, , melt butter and chocolate chips on low heat until melted. Remove from heat and add in eggs one at a time until incorporated. Add vanilla and milk.
Add the chocolate mixture to the dry ingredients and stir until combined. Spread batter into prepared pan and bake 35-40 mins. or until toothpick in center comes out clean. Cool completely in pan on cooling rack.