1. Separate eggs. Beat yolks in a large bowl. Add sugar and water; beat until fluffy.
2. Sift together flour and baking powder. Gradually add to eggs, mixing well. Then blend in vanilla extract.
3. Beat egg whites until they form peaks and are stiff but not dry. Fold into batter.
4. Line a cake pan (about 8 or 9 inches square and about 3 inches deep) with waxed paper or foil. Pour batter into pan. Rap the pan sharply on the table several times to remove large air bubbles.
5. Steam until done Test for doneness by inserting a toothpick: If no batter adheres, the cake is done.
6. Let cake cool slightly. Place a large flat platter over the pan and invert cake onto it. Remove waxed paper or foil. Turn the cake right-side up and cut in 2-inch squares