Have a large roasting tray ready and butter with a little of the melted butter. The tray should be about 30cm by 20cm. Pre heat oven to 180c.
To make the syrup, place the water and sugar in a saucepan and bring to boil, then to simmer adding the rose water for about 15 minutes or longer until the syrup is of rather thick consistency. Now add the lemon juice and zest and stir in.
To make the filling add the walnuts, caster sugar together and mix well. Add the ground almonds to the melted clarified butter and mix well.
Arrange a filo sheet in and then sprinkle with the with the ground walnuts and butter mixture, then cover with another filo sheet and again sprinkle with the almond and butter mixture, keeping going until you have 8 sheets of filo.
Now add a generous layer, about half of the chopped walnut and sugar mixture. Cover with 8 more layers of filo, again sprinkling in between each of them with ground almond and butter mixture. Follow with the second and final layer of chopped walnuts and sugar, pressing down gently. Finish with 8 more filo sheets sprinkled in between with ground almond and butter mixture. Butter the top layer and using a sharp knife, cut into small diamond shapes.
Spray with water and place in the oven for 30 minutes. Now reduce the temperature of the oven to 140c and cook the baklava for another 2 hours.
Cool completely and spoon the sugar and rose water syrup making sure that you cover all of the pastry with the hot syrup. Cover loosely and allow to settle for 48 hours in a dry place.