Step 1Dissolve the yeast and sugar in one-fourth cup warm water (105 to 115 degrees) and set it in a warm place.
Step 2If the egg is cold from the refrigerator, cover it with hot water and let it sit a few minutes to bring it up to room temperature. Combine 1 cup of the flour and the salt in a bowl and make a well. Break the egg into the middle of it; add the creme fraiche and pour in the yeast mixture, which should be foamy with bubbles. Mix everything together with a wooden spoon to form a smooth, soft dough, adding more flour as necessary. Dust it with flour, gather it into a ball, set it in a clean bowl and cover. Let the dough rise in a warm place, 45 minutes to an hour. If you are not ready to shape the dough at this time, punch it down and let it rise again.
Step 3Flatten the dough, place it in the center of the tart pan, and press it out to the edge using either your knuckles or the heel of your hand. Add only enough flour to keep the dough from sticking. If the dough shrinks back while you are shaping it, cover it with a towel, let it relax for 20 minutes, then finish pressing it out. It should be about one-fourth inch higher than the rim of the pan. It can be filled immediately or refrigerated until needed.
Step 1Cut the chard leaves away from the stems and save the stems for another purpose. Chop the leaves into pieces roughly an inch square, wash them in a large bowl of water and set them aside in a colander.
Step 2Heat the oven to 375 degrees. In a wide skillet, heat the butter and oil over medium heat; add the onion and cook it until it is translucent and soft, about 6 minutes. Add the garlic, the chard leaves (by handfuls, if necessary, until they all fit) and the salt. Turn the leaves over repeatedly with a pair of tongs so that they are all exposed to the heat of the pan and cook until they are tender, 5 minutes or more. When the chard mixture is cooled, squeeze out any excess moisture with paper towels.
Step 3To make the custard, beat the eggs, then stir in the half and half, infused saffron, lemon peel, grated Parmesan, a few scrapings of nutmeg and the parsley. Stir in the chard and onion mixture. Season with more salt, if needed, and freshly ground black pepper.
Step 4Toast the pine nuts in a small pan over medium heat until they are lightly colored, 2 minutes. Pour the filling into the tart shell and scatter the pine nuts over the surface. Bake until the top is golden and firm, about 40 minutes.