Preheat oven to 180 degree C. Line a 20 cm square baking pan with parchment paper and oil it well and set aside.

Take butter in a sauce pan and melt it lightly. Add in chopped dark chocolate and melt it gently till the chocolate is melted.

Now take it off the heat and add in one egg at a time and whisk well.

Now add in sugar, vanilla, salt and mix well.

Add in flour and fold gently,

Add in white and semi sweet chocolate chips and fold gently.

Spoon this into the prepared pan and bake it for 30 to 45 mins.

Now remove it and let it cool completely.

Cut into squares and serve.