Preheat the oven to 180°C, 350°F, Gas 4, and line 2-3 baking trays with baking parchment.
In a large bowl, cream the butter and caster sugar together until pale, then stir in the condensed milk. Sift the flour into the mixture and, using your hands, work it into a soft dough, incorporating the white and dark chocolate chunks.
Take a small handful of dough and flatten it with your fingers. Place 2-3 raspberries in the centre of the cookie and fold over the sides of the dough to encase them. Make the rest of the cookies in the same way.
Place the cookies on the baking trays with plenty of space between them and bake in the preheated oven for 15-18 minutes, or until golden brown but still a little soft.
Leave to cool slightly and set before transferring to a wire rack to cool completely.