Preheat oven to 350° F.
Shingle potato slices in bottom of 9 x 9-inch baking dish. Sprinkle with 1/2 teaspoon of salt and 1/4 teaspoon of pepper; set aside.
Cook bacon in 12-inch skillet over medium heat until crispy, 12 to 14 minutes. Using slotted spoon, transfer bacon to paper towel–lined plate.
Carefully add sausages to now-empty skillet and cook until lightly browned on tops and bottoms, about 5 minutes. Transfer to paper towel–lined plate.
Pour off all but 2 tablespoons fat from skillet and return to medium heat. Add onions, thyme, 1/2 teaspoon of salt, and 1/2 teaspoon pepper. Cover and cook until onions are softened, 7 to 9 minutes, stirring occasionally and scraping up any browned bits.
Add chicken broth and vinegar, scraping up any browned bits, and bring to simmer.
Carefully pour onion mixture over potatoes, spreading onions into even layer.
Place sausages, browned side up, on top of onions. Transfer to oven and bake until paring knife inserted into potatoes meets little resistance, about 1 hour and 15 minutes to 1 hour and 45 minutes.
Remove from oven and let cool for 10 minutes. Sprinkle with parsley and reserved bacon. Serve.
Yield: 3 to 5 servings. (See Tip 5)