For the pierogi dough: Add sour cream, salt, eggs and 1 cup water to a 4-quart or larger mixer with a dough hook attachment. Mix on medium to low speed until thoroughly combined.
Turn speed to low and slowly add the flour in 1-cup increments. Push down dough on sides of the bowl with a rubber spatula. Allow each cup to thoroughly mix in before adding the next cup. Add last cup slowly.
Dough should begin to pull away cleanly from the sides and bottom of the bowl. If it doesn't, slowly add more flour until it does. If your dough is too dry, add a little water to moisten. Once dough pulls away cleanly from the sides and bottom of the bowl, allow the dough hook to knead the dough until lightly tacky and soft, about 4 minutes.
Wrap dough in plastic wrap and refrigerate for at least 3 hours or up to overnight.
For the duck confit: Mix salt, both sugars and sumac in a large mixing bowl by hand until thoroughly combined.
Pat dry duck legs and rub with crushed juniper berries and crushed garlic. Set legs aside.
Cover the bottom of a deep-walled baking dish large enough to hold the legs in a single layer with 1 quart of the salt-sugar mixture, ensuring that the bottom of the dish is covered (add more mixture if necessary).
Put half of the fresh thyme sprigs down on top of the mixture. Snugly fit the rubbed duck legs in the mixture in a single layer. Cover with any remaining garlic or juniper berries that may have fallen off during placement. Cover the duck legs with the remaining fresh thyme. Pack with remaining salt-sugar mixture until meat of the dug legs is completely covered. Cover with plastic wrap and refrigerate for 24 hours.
Remove duck legs from refrigerator and gently rinse each leg over a sink running cold water. Pat dry with paper towels and set aside.
Place duck legs in a pot on stovetop and cover with schmaltz. Simmer on low heat until the meat pulls easily from the bone, about 2 hours. Pull duck legs from pot and allow to cool. Reserve oil.
Pull the meat from the bone and rough chop the duck leg meat. Reserve the bones.
For the duck stock: Place reserved bones in a 4- to 6-quart stockpot with the carrots, celery and onion. Add enough water to cover the bones and vegetables (about 4 quarts), then add the bay leaves and peppercorns. Bring just to boil and immediately adjust heat to low. Allow to simmer on low for 3 to 4 hours. Strain off bones and vegetables, reserving the dug leg stock.
For the pierogies: Cover potatoes with 1 quart duck stock or enough stock to cover. Bring potatoes to a boil, then immediately lower heat to medium. Simmer the potatoes until they are fork tender, about 20 minutes. Strain and spread on a sheet tray.
Sprinkle potatoes with 1/2 tablespoon kosher salt and allow to cool. Place potatoes and chopped duck leg meat in a mixing bowl. Add 1/4 cup reserved oil from the duck leg confit and fold in green onions. Taste filling and adjust seasoning if necessary.
Remove dough from refrigerator and allow to rest at room temperature for 15 minutes. Unwrap and quarter the dough with a bench scraper. Cover the remaining 3 quarters of dough with a towel while you work on the first quarter.
Roll the dough on a floured surface into an even sheet about 1/8-inch thick. Cut out dough discs using a 3- to 4-inch biscuit cutter.
Combine cornstarch and 1 cup water in a bowl. Moisten each disc with a thin layer of the cornstarch slurry. Place a heaping tablespoon of filling into the center of each disc. Gently pick up each disc by the sides, then pinch the dough around the filling. Pinch dough closed, sealing the filling inside. Place filled pierogies on a generously-floured sheet tray.
Bring large pot of salted water to a boil. Working in batches, gently place the pierogies in the boiling water. Return water to a boil and allow pierogies to boil until floating and warmed through, 10 to 15 minutes. Pull pierogies from the water and allow to dry slightly. (At this point you may refrigerate or freeze any pierogies you aren't planning on using.)
Prepare a saute pan over medium-high heat with 2 tablespoons of the reserved oil from the duck leg confit. Carefully fry the pierogies until the sides are light brown and crusty.
Serve with Pierogi Sauce.
For the roast tomato ketchup: Preheat the oven to 350 degrees F.
Toss tomatoes with oil, garlic, salt, basil, oregano and pepper and place on a sheet tray. Roast until tomatoes are half their size and browned, about 1 hour.
Puree tomatoes and any remaining liquid in a food processor with tomato paste until smooth. Store in an airtight container in the refrigerator.
For the sauce: Prepare a large saucepan at medium-high heat. Add duck fat to saucepan.
Saute mushrooms in saucepan until browned, 15 to 20 minutes. Add 3 tablespoons roast tomato ketchup (save the remainder for another use) and lightly brown the ketchup, 3 minutes. Add blanched carrots, celery, onion and duck stock. Bring to a boil, then simmer over medium heat until reduced by half. Season to taste.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Perly's Delicatessen, Richmond, VA