Grease a 13×9 pan (bottom & sides) and set aside.

Mix well the walnuts, sugar and cinnamon in a bowl and set aside.

Preheat oven to 300 degrees. Place a pan of water on the bottom rack.

Carefully lay the full-size phyllo sheet into the greased pan, folding over the pan edges. With a pastry brush, liberally apply melted butter.

Lay a cut sheet of phyllo into the bottom of the pan, and with a pastry brush liberally apply melted butter. Repeat 9 more times, so that you have the one full sheet and 10 smaller sheets as your bottom layer.

Sprinkle 2 cups of the walnut mixture into the pan. Lay 6 more sheets of phyllo on top, making sure to liberally apply the melted butter between each sheet. Repeat this 3 more times, so that you have 4 separate layers of the walnut mixture. For the top layer place as many phyllo sheets on top as you have remaining, again making sure to apply butter between each sheet.

Using a sharp plastic spatula, carefully fold over the large sheet of phyllo that should still be extended over the edge back onto the top, so that you can see down the inside edges of the pan. Using a sharp serrated knife, carefully score the baklava into whatever shape you want. A diamond pattern is the traditional shape. Try to cut about half-way down into the baklava. Bake for 2 ½ to 3 hours at 300 degrees until nice and brown. About 5 minutes before removing the baklava from the oven, combine the honey and lemon juice and heat over a medium heat until runny. Do not boil it, just heat it well so it has a consistency more like water. Remove the baklava from the oven and very carefully drain the butter if there is any extra.

Set the baklava on a cooling rack, and pour the honey mixture completely over it. Cover the baklava and let sit for at least 4 hours. Overnight is best. When you are ready to cut the pieces, cut through the score marks with a sharp knife, and use a spatula to remove the pieces.