Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4. Grease and line an 18cm (7in) square cake tin with greaseproof paper or parchment.
Spread 250g (9oz) fresh or frozen raspberries )in an even layer in the bottom of the tin.
Melt 50g (2oz)white chocolate in a bowl over a pan of hot water, ensuring the water doesn't touch the base of the bowl. Set aside allowing it to cool a little.
Beat 125g (4oz) butter and 125g (4oz) sugar together until light and fluffy, then beat in ½tsp vanilla extract. Gradually add 2 beaten eggs a little at a time, beating well after each addition.
Stir in 1 tablespoon milk, then sieve 125g (4oz)into the bowl and fold in with a spatula or large metal spoon. drizzle the melted white chcolate over the cake batter and mix together gently.
Spoon the prepared cake batter over the layer of raspberries and spread out to level, taking care not to disturb the raspberries beneath. Use the back of a spoon to make a slight indentation to the centre of the batter. This will help it bake level.
Bake in the centre of the oven and bake for about 45 - 50 minutes until golden brown, slightly pulling away from the sides and a cake skewer inserted in the centre comes out clean.
Allow the cake to cool in the tin for about 5 minutes before carefully turn out onto a wire rack to cool completely. The raspberries will now be the top of the cake.
To decorate melt a little more white chocolate as before, and drizzle the chocolate over the top of the raspberries.