green Swiss chard, stems and center ribs discarded
finely grated fresh orange zest
pine nuts , toasted (1 1/2 ounces)
sheet puff pastry
leek, sliced thin and chopped
Bring raisins and water to a boil in a 1-quart heavy saucepan. Remove from heat and let stand, covered, 1 hour. Drain in a colander. Pat dry using paper towels. Put oven rack in middle position and preheat oven to 400°F.
Blanch chard in a large pot of boiling salted water, uncovered, stirring occasionally, until tender but still bright green, about 3 minutes. Transfer chard with a slotted spoon to a large bowl of ice and cold water to stop cooking. Drain chard in a colander, then squeeze out excess water by handfuls. Coarsely chop chard.
Whisk together egg, milk, zest, and a pinch of salt in a large bowl. Stir in pine nuts, raisins, and chard until combined.
Sauté chopped leek in 1 tsp. olive oil until soft. Stir into egg mixture.
Roll out one thawed, puff pastry sheet on a lightly floured surface with a lightly floured rolling pin - very thin. Cut out an11-inch circle and fit into tart pan (do not trim edges). Chill shell while rolling out top.
Roll out smaller piece of dough on a lightly floured surface with lightly floured rolling pin into a 11-inch circle. Spread chard filling evenly into shell, then top with second piece of dough. Seal tart and trim edges, Brush with egg wash. Bake until top is golden, about 40 minutes. Transfer to a rack, cool slightly, then remove side of pan. Serve warm or room temperature.