Line a baking sheet with parchment paper.

In a microwave safe bowl, heat half the chocolate chips for 30 second intervals, stirring between each heat session, until melted.

Pour the chocolate onto the parchment lined baking sheet and spread out into a rectangular shape.

Place the baking sheet into the freezer for 10 minutes, while you work on the next step.

Heat treat the flour in the microwave for 60 seconds. Set aside.

Beat the butter, sugars, milk, and vanilla with an electric mixer in a large bowl, until smooth. Mix in the flour.

Remove the chilled chocolate layer from the freezer and drop the dough onto it, then spread evenly and press it down gently.

Melt the remaining chocolate just like you did the first time, then pour over the dough and spread to the edges.

Chill in the freezer for 10 minutes to set, then cut into pieces to serve.