Step 1Separate the leek greens from the whites, and finely chop the leek whites; reserve the leek greens. Separate the chard leaves from the stems, then cut the stems and 1 cup leaves into thin slices. Reserve the sliced chard stems and leaves for the broth and reserve the remaining chard leaves for the matzo balls.
Step 2Make the matzo ball dough: Heat 2 tablespoons schmaltz in a large skillet over low heat. Once the fat begins to shimmer, add the leek whites, garlic, allspice and a half teaspoon salt. Cook, stirring often, until translucent, about 5 minutes.
Step 3Add the reserved chard leaves and cook, stirring often, until the leaves are soft and all the liquid has evaporated, about 5 minutes. Transfer the mixture to a cutting board, cool for 5 minutes, and finely chop. Transfer to a medium bowl and stir in the currants, pine nuts and lemon zest.
Step 4Whisk the eggs in a large bowl until frothy, then slowly whisk in the remaining 6 tablespoons schmaltz, followed by the matzo meal, baking powder and 1 ½ teaspoons salt. Stir in one-third cup chicken stock just until combined. Gently fold in the cooked chard mixture until evenly distributed. Cover and refrigerate for at least 1 hour or up to 8 hours.
Step 5Meanwhile, make the broth: Heat the oven to 400 degrees. Put the lemons on a small baking sheet and roast until caramelized with dark spots, 35 to 40 minutes.
Step 6While the lemons roast, combine the shallots, bay leaves, cinnamon stick, stock and reserved leek greens and chard stems in a large, wide saucepot or Dutch oven and bring to a simmer over high heat. Cut the roasted lemons in half and squeeze their juice into the broth, then add the rinds to the pan. Simmer for 30 minutes.
Step 7Strain the broth through a fine-mesh sieve, discarding the solids, and return to the saucepot. Stir in the mint and 2 teaspoons salt. Taste and add more salt if desired. Bring to a simmer.
Step 8Use slightly wet hands to form the chilled matzo ball mixture into 20 equal-size balls. Drop them into the simmering broth. Once they float, cover and simmer until the balls puff up, 35 to 40 minutes. Stir in the reserved sliced chard stems and leaves and simmer until tender, about 5 minutes more.
Step 9To serve, ladle the soup and matzo balls into bowls and garnish with the dill.