Stir the sugar and water in a medium saucepan over medium heat until the sugar dissolves. Increase the heat and boil until the syrup turns deep golden brown, occasionally brushing down sides of pan with wet pastry brush and swirling pan, about 10 minutes. Remove from the heat and mix in the vinegar. Add the juices and boil until reduced to 1/2 cup, stirring occasionally, 15 minutes. Add the chicken stock, bring to a boil until reduced to 3/4 cup, about 20 minutes. Set aside.
In a small saucepan, cover the potato pieces with plenty of water and bring to a boil. Cook until the pieces are very tender but not falling apart, about 15 minutes. Drain the potatoes and run through a food mill. Set aside and allow to cool.
Dissolve the yeast in the warm water. Place the flour on a clean work surface and make a large well in the center. Pour in the water and yeast mixture, the beaten eggs, and salt. Add the milled potato and pork fat, and begin to work these ingredients into the flour, bringing it all together to form a soft, sticky dough. Add more flour if necessary to bring it all together. Set aside in a clean bowl, cover with a damp towel, and let rise in a warm place for 1 hour.
After 1 hour, punch down the dough and divide into 2 even pieces. Knead the dough a bit and set each piece aside again, covered with the damp towel, to rise another 45 minutes.
Preheat the oven to 475 degrees F.
Place the loaves in bread pans or form them into rounds on baking sheets and bake for 35 to 40 minutes, until the bread is nicely browned on the outside. Let cool 10 minutes before slicing.
While the bread cools, return the citrus sauce to the heat and bring to a simmer. Add the segmented fruit, peel, and butter, and cook 10 minutes to thicken and heat through. Serve the sauce spooned over the bread.
In a large, heavy-bottomed saucepan, heat the oil over high heat until smoking. Add all the chicken parts and brown all over, stirring to avoid burning. Remove the chicken and reserve. Add the carrots, onions, and celery to the pot and cook until soft and browned. Return the chicken to the pot and add 3 quarts of water, the tomato paste, peppercorns, and parsley. Stir with a wooden spoon to dislodge the browned chicken and vegetables bits from the bottom of the pan. Bring almost to a boil, then reduce heat and cook at a low simmer until reduced by half, about 2 hours, occasionally skimming excess fat. Remove from heat, strain, and press on the solids with the bottom of a ladle to extract out all liquids. Stir the stock to facilitate cooling and set aside. Refrigerate stock in small containers for up to a week or freeze for up to a month.
Yield: 1 1/2 quarts