Preheat the oven to 320°F.  Line an 8 inch square baking pan with parchment paper, or spray with non-stick cooking spray.  Set aside.

Place the butter and semi-sweet chocolate in a microwave safe bowl.  Microwave for 30 seconds at a time, stirring in between, until the chocolate has just melted.

Add the granulated sugar, brown sugar, eggs and vanilla extract to the chocolate mixture.  Mix until well combined.

Add the flour, cocoa powder and salt and mix until just combined.  Gently fold in the milk and white chocolate chunks.

Pour the brownie batter into the prepared baking pan.  If desired, sprinkle a few more white chocolate and/or milk chocolate chips on top just before baking.

Bake for 25 minutes, or until the sides and top have just set but the center is still soft.  Allow to cool in the pan for 30 minutes before slicing into squares.