Preheat oven to 350 degrees Fahrenheit.
Mix together that cup of butter, brown sugar, and flour.
Press in an 8 x 8 pan.
Pop it in the oven and bake for 25 minutes.
Once done, set aside to cool a bit while you make the next layer.
In a medium-sized saucepan dump the can of condensed milk into it. Add the 1/4 cup of butter and tsp of vanilla. Whisk together on medium heat for about 6 minutes. Make sure to stir it frequently so it doesn't burn.
Pour over the bottom layer of your cookie Squares. Spread around with a spatula so that the first layer is completely covered with the condensed milk mixture.
Put it back in the oven and bake for 17-18 minutes.
Take it out and sprinkle the chocolate chips over it evenly. Let it sit for 5 minutes. After five minutes spread the chocolate evenly across the cookie bars with a spatula.
Let them cool completely before cutting into them. I prefer to put them in the fridge once they cool to help firm them up.