Preheat the oven to 350 degrees. Line a 9” square baking pan with aluminum foil with enough overhang on each side to easily remove the bars from the pan once baked. Spray with cooking spray and set aside.
In a medium sized bowl, stir together the flour, corn starch, sugar, salt, and lemon zest. Using a pastry cutter or the backs of two forks, cut the diced butter into the dry ingredients until it becomes a coarse meal consistency with pea-sized clumps. Bake in the preheat oven for about 15 minutes, or until the crust is set and then edges have just started to turn golden. Do not overbake. Set aside the cooked crust while you prepare the filling.
Combine the butter, brown sugar, honey, vanilla, and salt in a small saucepan. Cook over medium-low heat, stirring until the butter and sugar have dissolved. Once melted and no graininess from the sugar exists any longer, increase the heat to medium and bring to a boil, boiling for 3 minutes. After three minutes have passed, remove the pan from the heat. Add the chopped walnuts, pistachios, heavy cream, and spices to a medium sized bowl and stir in the butter mixture until evenly combined.
Spread the warm filling over the crust and smooth out. Bake in the preheated oven for about 20 minutes, or until the edges and parts of the center are bubbling and the bars have turned caramel in color. Allow the bars to cool completely prior to removing from the pan (you can speed this process up in the fridge). Remove from pan by pulling out the foil liner. Gently melt the white chocolate chips on a double boiler sitting over LOW heat. Be careful to not melt at too high of heat or your white chocolate may seize. Drizzle over the top of the bars. Cut into 16 bars and serve at room temp.