2pinchesfine grain sea saltplus extra for sprinkling slices
Preheat oven to 350F.
Combine the black walnuts, pecans, pistachios, brown sugar, cinnamon and salt in a large bowl. Toss the ingredients together so that all the nuts are coated with the sugar, cinnamon and salt. Brush a 9-inch pie plate with some of the melted butter. (I used a tart pan with a non-removable bottom).
Unroll the Filo dough. Drape a piece of plastic wrap over it and cover it with a damp towel to prevent it from drying out. Layer 8 sheets of Filo in the prepared pie pan, brushing each layer with butter and rotating sheets to cover the pie plate. Allow the edges to overhang the sides. Sprinkle a third of the nut mixture over the layered Filo.
Layer four sheets of Filo over the nut mixture in the same manner; sprinkle with a third of the nut mixture. Repeat these last two steps. Top with an additional eight sheets of Filo, again, brushing, buttering and rotating the sheets. Fold the end of the overhanging Filo up over the top of the pie. Brush with butter.
Using a sharp knife, cut the pie into eight wedges. Cut 1-2 additional sheets of Filo into thin strips; arrange decoratively on top of the pie. (Save remaining Filo for another use). Bake pie for 40 to 45 minutes or until golden brown.
Meanwhile in a saucepan, combine the sugar, water honey and salt. Bring to a boil; reduce heat. Simmer uncovered for 10 minutes. Remove from heat and add vanilla extract. Pour the syrup over the warm pie. Let the pie cool in the pan.
Sprinkle each slice of pie with a pinch of sea salt before serving.