Make the syrup
Dissolve the sugar in the lemon juice and water in a saucepan over medium heat. Simmer for 10 minutes.
Remove from the heat and whisk in the allspice, rosewater and orange blossom water. Let cool completely.
Make the filling
Preheat the oven to 350F. Coat the bottom and sides of a 9-by-9 inch square baking dish with butter.
Melt 3 tablespoons of the clarified butter in a saute pan over medium heat. Add the sesame seeds and saute until golden brown, stirring frequently. Remove from the heat and add the pistachios, currants, sugar, cinnamon, nutmeg and fleur de sel. Stir to combine. Set aside.
Melt the remaining clarified butter in a saucepan over low heat.
Carefully role open the phyllo dough. Cut the sheets in half, crosswise. Stack the dough sheets on top of each other, cover with a sheet of plastic wrap and place a damp cloth on top. This will keep the dough from drying out while you are assembling the layers. Phyllo dough is best handled when slightly moist but not soggy.
Place two sheets of the dough in the bottom of the buttered pan. Re-cover the stacked dough to keep it from drying and repeat throughout the assembly.
Brush the surface of the dough with the melted butter using a pastry brush. Add two more sheets of dough and apply another coat of butter. Continue until you have a total of eight layers.
Using a spoon evenly spread half of the filling over the surface of the dough layers. Add eight more layers of dough and butter. Spread the remaining filling over this layer and cover with eight more layers of dough. Brush the top layer of the dough with the remaining butter.
Using a sharp knife and being careful not to distort the layers cut the baklava into 2-inch squares. Bake on the middle shelves of the oven for 30 minutes. Lower the heat to 300F and bake for an additional 45-50 minutes until the surface is a deep golden color.
Remove from the oven and let cool for a few minutes. Pour the syrup evenly over the top and set aside to cool completely.
Store in an airtight container at room temperature for up to one week.