Rub roaster inside and out with lemon. Cut yellow onion in half and stick with cloves; place in cavity of roaster. Truss bird and season with salt and pepper; place in 8-quart Dutch oven or saucepot. Pour in chicken broth and enough water to reach halfway up sides of roaster; add bay leaf. Place over medium heat; bring liquid to a simmer. Cover and simmer, allowing 20 minutes per pound. (To keep meat tender, do not allow to boil.) During last 45 minutes cooking, add white onions and carrots. Roaster is done if juices run clear when thickest part of thigh is pierced with a fork. Remove chicken and vegetables to serving platter and keep warm.
Add more broth or water to poaching liquid, if necessary, to bring it halfway up sides of Dutch oven; bring to a boil. Meanwhile, prepare dumplings: In medium-sized bowl, combine flour, warm water and 1 teaspoon salt; mix well. Turn dough out onto well-floured surface; knead 4 to 5 minutes until it becomes elastic, reflouring board as necessary. With sharp knife, cut into 1 1/2 to 2-inch squares. Add squares to boiling poaching liquid and cook 5 to 7 minutes until "al dente". Remove dumplings to serving bowl. Over high heat, cook poaching liquid until reduced and slightly thickened. For a thicker gravy, stir a small amount of flour blended with 1 cup cold water into poaching liquid. Serve roaster with vegetables and dumplings. Pour some gravy over dumplings; pass remaining gravy separately.