Preheat oven at 250ºC. Take a bowl and put eggs and beat until it becomes a little bit foamy. Take another bowl and put sugar and butter and mix with spoon, then add this butter in three parts in eggs while beating. Now mix baking powder in flour and put this flour in egg mixture, gradually, and beat well. Also add vanilla essence and mix well. The mixture should look like thick custard. Now put this mixture in cake pan and put it in the oven and reduce the oven temperature from 250ºC to 200ºC and bake until the cake rises about an inch, then reduce temp from 200ºC to 150ºC and bake until it is done. Then take it out from the oven and let it cool down for about 10 min, then cut in slices and again bake until crispy and golden brown, increase oven temp from 150ºC to 200ºC. Now enjoy Cake Rusk with tea.