1. Position rack in the centre of the oven and preheat oven to 180ºC . 2. Brush the inside of a 23 cm Bundt or springform tube pan with oil and sift a little cocoa over the pan. Tap out the excess. 3. Sift together flour, one third cup plus 1 tablespoon sifted Dutch-process cocoa, sugar, baking powder, salt and cinnamon into a large mixing bowl. 4. Make a well in the centre of the dry ingredients and add oil, half cup plus 2 tablespoons warm water, vanilla and egg yolk. Do not mix. 5. Place egg whites in another large mixing bowl. Add cream of tartar and beat with an electric mixer until they are white and foamy. Add 2 tablespoons confectioners' sugar and continue beating until stiff but not dry. Scrape off the beaters and, without washing them, place them in the flour-and-oil mixture and beat at low speed just until well blended. In four additions, gently fold this mixture into the egg whites. 6. Turn the batter out into the prepared pan and smooth the top with a rubber spatula. Rap the pan sharply on the counter once to remove any large air bubbles. 7. Bake for 40 to 45 minutes, or until the top feels springy and a cake tester inserted in the centre comes out clean. (The top of the cake will be cracked.) 8. Cool the cake upright on a wire rack for 10 minutes. With a knife, loosen sides and centre of cake from the pan. Invert onto the rack, lift off pan and cool cake completely. Place on a serving platter and top with a light sifting of confectioners' sugar. Serves 16.