n the bowl of a large stand mixer, cream the butter and the brown sugar until light and fluffy, about two minutes. Beat in the vanilla.
Slowly add the flour, scraping down the sides as necessary.
With the mixer still running, slowly add in the sweetened condensed milk. You may need to stop the mixer periodically to scrape down the sides.
Once it is fully combined, stir in the mini chocolate chips.
Melt 1 1/2 cups milk chocolate chips. While they are melting, like a 10 by 15 pan with wax paper. Spread the melted chocolate over the wax paper, being careful not to make it too thin (you won't be able to cover the whole surface area of the pan.
Refrigerate for 15 to 30 minutes.
Spread the cookie dough over the hardened chocolate in an even layer. Refrigerate 15 to 30 minutes.
Melt the remainder of the chocolate, and pour over the cookie dough layer. Allow to harden and then break apart.