Beat eggs, sugar, flour, vanilla essence, ovalette and condensed milk by using high-speed electric mixer until the mixture is pale, fluffy and double in volume. Slowly drizzle the melted butter onto the cake batter and keep on whisking it by using slow-speed electric mixer until everything is just well combined. Divide the mixture into two equal portions. Add pandan paste/juice and green food colouring into one portion and mix well. Pour the white and green cake batters alternately into a square baking pan already lined with parchment paper. Bake the cake at 150-160 degree Celsius in a preheated oven for about 45 minutes. Remove the cake from oven and let it cool in the baking pan for about 5 minutes. Cut the cake to mini squares when it is completely cooled.