Preheat the oven to 180°C/160°C fan /gas 4. Grease a 20- 23cm spring form tin, then line the base with nonstick baking paper.
For the streusel topping, melt Lurpak Baking in a small pan, then stir in the flour, salt and caster sugar. Mix with a wooden spoon to make a crumbly mixture, then gently fold in the flaked almonds.
To make the cake, put Lurpak Baking into a large bowl and beat with the sugar to make a light, creamy mixture using an electric whisk or wooden spoon. Next, beat in the eggs one at a time. If the mixture starts to curdle, add a spoonful of flour. Add the vanilla extract and the optional rosewater. Then, using a large metal spoon, gently fold in the remaining flour and baking powder. If the batter is not of dropping consistency, add a little milk.
Spread the mixture in the tin, and with a back of a moistened spoon, make a small hollow in the centre and dot with the raspberries or blueberries. Cover with the streusel mixture and bake in the oven for 45-60 minutes until golden brown - an inserted skewer should come out clean. Leave the cake to cool in the tin for 15 minutes and then remove.
For the white chocolate drizzle, melt the chocolate in a heatproof bowl over a pan of simmering water and use a fork to drizzle the white chocolate over the cake.