In a medium bowl, stir together the melted butter, light brown sugar, caster sugar, milk and vanilla bean paste. Continue stirring until the mixture is combined and forms a syrupy brown liquid.
In a medium sized mixing bowl, whisk together the remaining ingredients - flours, baking powder, baking soda and salt.
Use a spatula to decant all of the butter mixture into the flour mixture. Use a spoon to start combining the mixture, starting in the centre and moving outwards. Continue until a dough forms. The dough should be just too sticky to hold together in a ball - it should adhere to the side of the bowl as you stir it. If it's more solid than that, add a teaspoon or two more milk. If it 'melts' into the bowl and forms a flat surface, it's too wet. Add 10-15g white rice flour, mix thoroughly, and pop it back in the fridge.
Cover the dough and place it into the fridge for one hour. While you're waiting, chop the chocolate and line two baking trays.
After 1 hour, mix the chopped chocolate into the dough. Use your hands to divide the dough into 12 balls of dough, about a tablespoon worth each. Divide the cookies evenly between the two trays, then place the trays back into the fridge while the oven preheats. If you don't have room, putting them all on a plate is fine.
Preheat the oven to 180C/350F. Bake one tray of cookies at a time for 12-25 minutes or until cooked through and lightly browned. Allow them to nearly completely cool before eating (they are fragile before cooling).