Preheat the oven to a temperature of 325 degrees Fahrenheit. Employ a nonstick spray on a 9x13-inch baking pan to ensure a non-adhesive surface.

Utilize a medium glass bowl to melt the chocolate. This should be achieved through intermittent heating in a microwave for 30-second durations, stirring after each interval. Once the chocolate is melted and possesses a smooth consistency, set it aside to allow a slight decrease in temperature.

In a capacious mixing bowl, combine the melted butter with the light brown sugar by whisking them together. Proceed to incorporate the eggs and vanilla extract into this mixture, whisking thoroughly.

Introduce the melted chocolate into the mixture, ensuring a homogeneous blend. Subsequently, incorporate the flour, taking care to mix only until the ingredient is just combined to avoid over-mixing. Conclude by folding in the miniature chocolate chips.

Transfer the batter into the prepared pan and proceed to bake for a duration of 25 to 35 minutes. It is critical to monitor the baking process closely and remove the pan from the oven when a toothpick inserted into the center emerges clean. Allow the brownie layer to cool completely.

In a medium-sized mixing bowl, utilize an electric mixer to blend the room temperature butter, light brown sugar, and white sugar until the mixture is light and fluffy. Incorporate the milk and vanilla extract into this mixture.

Gently mix in the flour until just combined, ensuring not to overwork the mixture. Note the recipe's NOTES concerning the flour's preparation. Fold in the miniature chocolate chips.

Once the brownie layer has cooled, spread the cookie dough layer evenly over it. Place in a refrigerator to solidify the dough, making it firm. Alternatively, to expedite the firming process, the assembly may be placed in a freezer.

Utilizing a sharp knife, cut the firmed brownies into squares. It may be necessary to clean the knife with a paper towel intermittently to maintain a neat cut, due to the dough's tendency to adhere.

If a chocolate drizzle is desired, melt the semisweet chocolate chips with shortening in a microwave; stirring the mixture until smooth consistency is achieved.

Decant the melted chocolate into a small zip-sealed bag, trimming off a corner to create an opening. Apply pressure to the bag to drizzle the chocolate atop each brownie. If desired, extra chocolate chips may be sprinkled on top as a finishing garnish.