In a large bowl, blend together the butter and the sugar. Separate 3 of the eggs; add the yolks and the 2 remaining whole eggs to the butter mixture. Stir in the vanilla and water.
In another bowl, sift together the baking powder and flour. Add these dry ingredients to the creamed mixture.
Whisk 3 egg whites until they are foamy. Add 1 tablespoon sugar. Continue to whisk the whites until they are stiff, but not dry. Fold whisked whites into batter.
Pour the batter into a greased 25cm ring tin. Wrap a large coin in foil then place the coin in the batter. Press the coin down; it should be completely hidden. Sprinkle the nuts and seeds on top of the batter.
Bake the cake for about 70 minutes, or until done. Cool on a wire rack.