In a large mixing bowl using a mixer (stand or hand) combine butter, vanilla extract, and brown sugar.
Mix it very well until it is all crumbly.
Next, add in flour and again mix to combine again with a mixer of choice.
The dough will be crumbly, if it is powdery, add a few tablespoons of water (up to 3) to correct.
Press dough firmly and evenly into pan.
Top with a scattering of chocolate chips.
I then added sprinkles to this layer *OPTIONAL
Cover and refrigerate while you prep the next step.
In microwave-safe bowl place chocolate and melt (per directions on package)
Stir to ensure it is all melted without lumps or chunks.
Next, add in condensed milk and again stir to combine.
Remove covered pan from refrigerator, and cover the entire surface with chocolate.
Cover again.
Refrigerate to set. (1 hour)
After an hour remove from refrigerator and cut into portions.
Keep any uneaten portions both covered and refrigerated for up to 5 days.