Prepare the prunes: in a wide, medium saucepan, boil the apple juice over high heat until reduced to about 1¼ cups. (If using grape juice, warm it without reducing.) Add the prunes and vanilla, and cook over medium heat until very tender, 10 to 15 minutes. You should have no more than about 14 cup of liquid left in the pan; if needed, reduce the liquid for a few minutes over high heat.
Meanwhile, break the matzohs into small pieces in a bowl. Sprinkle with 14 teaspoon cinnamon and the salt. Pour the wine or grape juice over the matzohs and stir until all the liquid is absorbed. Beat the eggs until light and foamy and add to the matzoh mixture. Stir well and set aside for a few minutes to soak the matzohs (the eggs will not be totally absorbed). In a small bowl, combine the remaining 14 teaspoon cinnamon and the brown sugar and set aside.
Please read “Making Matzoh Brie” and choose the cooking style you prefer. In a 10- to 12-inch heavy skillet (preferably nonstick—the sugar from the prunes will make this matzoh brie somewhat sticky) heat the butter until it sizzles. Add the matzoh and egg mixture all at once. As it begins to set and brown, break it up into largish pieces with a spatula, turning and browning them on both sides. Spoon the stewed prunes and their liquid over the cooked matzoh brie, as a topping. Or you can incorporate the prunes into the matzoh brie: when the matzoh brie is nearly browned, add the prunes and their liquid. Continue lifting and turning until all the matzoh pieces are golden brown and well combined with the prunes. If you prefer a fluffier matzoh brie, lightly fry the matzoh sections until just cooked through on all sides, adding the prunes about halfway through the cooking process.
Sprinkle with the cinnamon sugar. Top with plain yogurt, or if you prefer something richer, yogurt cream or sour cream. It really needs no additional sweetening, but if you wish, serve it with maple syrup, preserves, or honey.