1. Brown butter in a saucepan until the milk fats have separated and browned. Pour into a separate mixing bowl.
2. Add sugar and beat until combined.
3. Add the eggs and cookie butter into the mixing bowl.
4. Beat the mixture with electric beaters for 4 to 5 minutes until pale and thick.
5. Add in the flour, chopped white chocolate and broken biscuits and fold through.
6. Pour batter into a lined baking pan and smooth out with an offset spatula.