How to Make It
In a food processor, pulse the flour with the salt. Add the egg yolks and olive oil; pulse until combined. Add the butter and pulse until the mixture resembles coarse meal. With the machine on, slowly add the water and process just until the dough comes together. Transfer the dough to a sheet of plastic wrap and pat it into a disk. Wrap the disk and refrigerate for at least 30 minutes.
In a large skillet, stir the onions with 3 tablespoons of the olive oil until thoroughly coated. Cover and cook the onions over moderately low heat, stirring occasionally, until they are very soft, about 30 minutes. Reduce the heat to low if the onions begin to brown.
Uncover the skillet. Increase the heat slightly and continue cooking, stirring frequently, until the onions become a rich golden brown, about 30 minutes longer. Remove the skillet from the heat.
Meanwhile, bring a large pot of water to a rolling boil. Strip the chard leaves from the ribs, leaving the leaves as intact as possible; reserve the ribs for another use. Blanch the chard leaves in the boiling water until softened, 1 1/2 to 2 minutes. Drain the leaves and refresh them under cold running water. Drain again and pat thoroughly dry.
In a spice grinder, combine the cinnamon stick with the cloves, ginger, nutmeg and pepper and grind to a powder. Add 1 1/4 teaspoons of the spice mixture to the onions and stir until evenly incorporated; reserve the remaining mixture for another use. Season with salt.
In a small bowl, using a wooden spoon, lightly beat the goat cheese with the crème fraîche and 1 teaspoon of salt until smooth.
Preheat the oven to 400°. Set the disk of dough between 2 large sheets of wax paper and roll out to a 12-by-15-inch rectangle. Transfer the pastry to a 9-by-12-inch ceramic baking dish at least 1 1/2 inches deep. Line the pastry with the chard leaves, allowing them to extend beyond the pastry overhang.
Using a spatula, spread the goat cheese mixture over the chard in an even layer. Spread the spiced onions over the cheese and sprinkle with the pine nuts. Fold the extended chard leaves and the pastry over the onion filling. Brush the pastry and the chard leaves with olive oil.
Bake the tart for about 40 minutes, or until the pastry is golden. Remove from the oven and transfer to a rack. Let cool for at least 30 minutes before serving warm or at room temperature.
This savory tart can also be assembled and baked free-form on a large rimmed baking sheet.