Cream the butter and sugar together for about 2 minutes, until light and creamy.
Add the oil and whisk for 1 minute until well combined.
Add the eggs and vanilla and whisk for about 2 minutes, scraping down the sides of the bowl as needed.
Add the yogurt and whisk for 1 more minute until smooth.
Sift the flour and baking powder directly into the same bowl.
Gently fold the mixture by hand.
Give a final gentle mix to ensure everything is evenly combined.
Separate about ⅓ of the batter into a different bowl.
Add the cocoa powder and the milk into the bowl.
Mix well.
Add the 2 batters with a spoon, into a lined baking pan.
Bake at 170°C (350°F) for 30–35 minutes, or until a skewer inserted in the center comes out clean.
Pour the simple icing glaze over the cake while it is still warm.
Drizzle the melted chocolate as you like.
Enjoy warm, or let it cool completely before serving.
