Preheat oven to 350 degrees F. Line a 9-inch square baking pan with parchment paper, allowing a bit to hang on either side, to make it easier to pull the bars out of the pan. Set aside.

To make the crust, in a large bowl, cream together the butter and brown sugar until creamy, about 5 minutes on high. Stir in the vanilla, lemon zest, and egg until well-combined. Add the flour and mix until just combined. Transfer the mixture into the prepared baking pan. Press down with floured hands, onto the bottom of the pan, in an even layer. Bake for 10 minutes, until lightly golden brown around the edges. Remove from the oven and let cool while you make the filling.

In a medium bowl, toss together the walnuts, pistachios, sugar, cinnamon and salt. Add the softened butter and toss together until well-combined and the mixture resembles coarse crumbs. Set aside.

Lay one sheet of phyllo on a cutting board. Brush with melted butter and then place another sheet of phyllo. Brush once more and repeat until all the phyllo sheets and butter have been used. Cut into thin strips using a pizza cutter or a sharp knife.

Transfer the nut mixture onto the par-baked crust, and spread out in an even layer. Sprinkle the top with the phyllo pieces. Bake until golden brown all around and the phyllo is golden brown and flaky, about 18 to 20 minutes.

While the bars bake, make the syrup topping. In a medium saucepan, combine the honey, butter, sugar, lemon juice, and spices. Set over medium heat and cook until melted through and the mixture comes to a low simmer. Remove from heat and stir in the vanilla.

Once the bars are baked, remove from the oven and immediately pour the syrup over the top evenly. Allow to cool completely and the bars have set, at room temperature, about 4 hours. Lift the bars from the baking pan, using the parchment paper, and transfer to a cutting board. Cut into three even rows. Then cut each row into 3 squares. Then cut each square in half diagonally so you end up with triangles. Serve with a drizzle of honey and sprinkling of pistachios. Leftovers can be stored in an airtight container at room temperature for up to 2 days. Enjoy!