Heat a large, heavy-bottomed pot, like a cast iron Dutch oven or braiser, over medium heat. Add the bacon, and cook until bacon is crispy, about 8 minutes. Using a slotted spoon, remove the bacon and set aside, leaving the fat in the pan.

Season the chicken with salt and pepper. Add olive oil to the bacon fat, then brown the chicken, turning drumsticks to brown all over. Remove chicken from pan and set aside. Drain all but 2 tablespoons of fat from the pan.

Add the onions into the pan and sauté over moderate heat until golden, about 8 - 10 minutes. Add the garlic, and cook for an additional minute.

Add tomato paste and cook for a minute or two, combining it with the onions and garlic. Add mushrooms and cook for a few minutes until mushrooms begin to release some of their liquid.

Add bay leaf and thyme to the pan. Pour in the wine and stock, and stir to combine. Return chicken to the pan, cover and reduce heat to medium low. Let chicken simmer for 30 minutes.

While the chicken is cooking, use a fork to blend together the butter and flour until it is a smooth paste. Set aside.

Using a slotted spoon, remove cooked chicken from pan and set aside. Increase the heat to medium high, then add the flour and butter paste to the pan. Let the sauce come up to simmer and cook until it is thickened, about 5 minutes. Sauce should coat the back of a spoon.

Remove skin from cooked chicken, then nestle it back into the sauce. Let it gently simmer, uncovered, for about 8 - 10 minutes. Sprinkle the crispy bacon on top, along with fresh parsley, if desired.

Remove bay leaf and stems from fresh thyme before serving.