- Bring a saucepan of lightly salted water to a boil over high heat. Add the onions and cook until the skins loosen, about 2 minutes. Drain the onions and rinse under cold running water. Slip off and discard the skins.
- Cut the chicken into 9 pieces, then season with the 1 1/2 teaspoons salt and the 1/2 teaspoon pepper.
- In a Dutch oven over medium heat, fry the bacon until crisp and browned, about 8 minutes. Transfer the bacon to paper towels to drain, leaving the fat in the pot.
- Increase the heat under the pot to medium-high. Working in batches, add the chicken, skin side down, and cook, turning once or twice, until lightly browned on both sides, about 5 minutes per batch. Transfer to a platter.
- Add the onions and carrots to the pot and cook, stirring occasionally, until lightly browned, about 3 minutes. Add the shallots and cook, stirring occasionally, until softened, about 1 minute. Carefully add the cognac and reduce the heat to low. Using a long-handled match, light the cognac and let the flame burn for 30 seconds, then cover to extinguish the flame. Uncover, add the Riesling and bring to a boil over high heat. Return the drumsticks, thighs and wings, and then the breasts to the pot. Reduce the heat to medium-low, cover and simmer for 35 minutes.
- In a heatproof bowl, mash together the butter and flour to form a thick paste. Gradually whisk about 1 cup of the hot cooking liquid into the flour-butter mixture, then stir this mixture into the pot. Simmer until the chicken shows no sign of pink when pierced with the tip of a sharp knife near the bone, 5 to 10 minutes more. Adjust the seasonings with salt and pepper. Crumble the bacon and sprinkle the bacon and thyme over the chicken.