Preheat the oven to 180 degrees. Grease the entire inside of your bundt tin, right to the edges.
Mix the sugar and butter together in a large mixing bowl.
Add roughly ¼ of the flour (through a seive) and mix, before adding one egg. Repeat alternating flour and eggs until you have a thick and creamy batter.
Add the baking powder, vanilla, and a small splash of milk to make the mixture moist.
Sift in the cocoa powder. You should now have a dark and rich mixture.
Pour ½ of the mixture into the bundt tin. Add your chocolatey pieces in the centre (equal distance between the edge and centre of the tin), going all the way around. This should create a circle of chocolate in your mixture.
Add the remaining mixture on top of your chocolate so it is buried in the middle.
Pop the tin into the oven for 25 minutes, checking with a skewer if the mixture is baked through. If not after 25 minutes, put it back in the oven and check after 5 minutes – repeat until the cake is thoroughly cooked. Leave to cool.
Later, remove the cake from the tin and place bottom-side-down on a cooling rack. Leave until the entire cake is cooled.
Melt the white chocolate by placing it in chunks in a glass dish, and heating this over a pan of boiling water. As soon as the chocolate is smooth, remove from the heat*. Using a spoon (or a piping bag with a narrow nozzle), drizzle the melted chocolate over the cake in whatever pattern you like. If your bundt tin has created defined lines around the top of the cake, see if you can use these in your decoration. Leave to rest so the chocolate sets.
*The cake in our picture has some splodges of white chocolate – this is what can happen if you let your chocolate melt for too long, as it will develop lumps! Make sure you check your white chocolate, stirring it while it melts to get the perfect smooth consistency.