For the baklava:

1. Preheat the oven 400 degrees. Grease a square baking dish with non-stick cooking spray.

2. Place walnuts, pistachios and cinnamon in a food processor. Pulse until the nuts are almost all crushed, but still have a few bigger pieces.

3. Take the 12 phyllo sheets and cut in half. Place one piece of phyllo in the bottom of the greased dish. Brush with butter and top with another piece of phyllo. Repeat seven more times for a total of 8 pieces of phyllo. Brush top with butter and then sprinkle with ⅓ of the nut mixture. Top with another piece of phyllo. Brush with butter. Repeat three more times for a total of four layers. Sprinkle with ⅓ of the nut mixture. Top with another piece of phyllo. Brush with butter, repeat three more times for a total of four layers. Brush top layer with butter. Sprinkle remaining nuts on top and top with another layer of phyllo. Brush with butter. Repeat seven more times for a total of 8 layers. Brush top layer with butter.

4. Cut baklava into 16 squares. Bake until golden brown, about 45 minutes.

5. While the baklava is cooking, make the syrup. In a medium saucepan, heat sugar, water, honey and lemon juice to a boil. Reduce to a simmer and cook until thickened, about 5 minutes.

6. Once the baklava comes out of the oven, let rest for 1-2 minutes then pour syrup over the top. Cover with plastic and let the baklava sit overnight.

7. Roughly chop up the baklava.
    

For the sundae:

1. Place generous pieces of the baklava as a base for the sundae

2. Add a scoop of pistachio ice cream.

3. Drizzle honey over ice cream.

4. Top with finely chopped pieces of the baklava and pistachio pieces. Additionally, a stick of cinnamon can be added for presentation.