Preheat oven to 170°C. Grease a square baking tray or a bundt.
Cream butter and sugar until light. Slowly add egg, one by one while mixing. Then add the durian flesh and mix well.
Carefully fold in the flour and the milk until all the flour is used up. Pour mixture into the greased baking tray and bake in preheated oven for about 40 minutes. Check doneness by inserting a skewer.
When done, remove from oven and let cool for 10 minutes before removing in from the baking tray.