Preheat the oven to 180°C (350°F) and prepare a cake tin (I used a rectangular one slightly larger than 8" x 8" or 20cm x 20cm).
Melt the white chocolate and set aside.
Using a mixer or electric whisk, beat the sugar and butter until light and fluffy.
Add the eggs one at a time, followed by the melted chocolate and vanilla extract.
In a separate bowl, mix the dry ingredients together.
Alternating between the dry ingredients and the milk, add them to the wet mixture, stirring until smooth.
Pour the batter into the prepared tin and bake for 25–30 minutes, or until a skewer or toothpick inserted in the centre comes out clean. Leave to cool in the pan.