Preheat the oven to 160 degrees C (320 degrees F). In a large bowl, combine the flour, sugar, cocoa powder, and baking powder. In a separate bowl, whisk the milk, vegetable oil, and vanilla extract. Add the wet ingredients to the dry ingredients and stir with a wooden spoon until just combined. Pour the batter into a greased and floured 22 cm (8 inch) pan. Bake for 40 minutes or until a toothpick inserted in the center comes out clean. Cool the chocolate cake on a wire rack and dust with icing sugar before serving