1) With a clean kitchen towel or paper towel, pat the guinea thighs dry. Season them with salt and freshly ground black pepper. Dredge in the flour and pat off all excess flour. Meanwhile, heat a large (30-cm) saute pan over medium heat for one minute, and then add the olive oil. It should be hot but not smoking by the time you are done flouring the guinea thighs.
2) Brown the thighs, skin side down first, adjusting the heat and adding more oil so that the meat sizzles at a nice pace. Cook until golden, 2 to 3 minutes, and then turn the meat and cook another minute or two to color the other side. If your pan is small, cook the thighs in two batches. Transfer the thighs to a plate.
3) You will now need a 1 litre straight sided saute pan or an enameled cast-iron Dutch oven. This pan should be wide enough to have the thigh pieces fit in single layer and deep enough to hold at least 1 litre of liquid (a stock pot will work in a pinch).
4) Put this pan over medium-high heat. Add enough olive oil to cover the bottom of the pan. Add the pancetta and sweat for 2 to 3 minutes. Add the onions and garlic and sweat for another five minutes or so, so that the onions are soft and translucent. Add the rosemary, sage, and a small pinch of pepper. (The pancetta should add enough salt to the sauce so don't worry about salting yet.) Sweat for one more minute.
5) Add the wine, 4 cups of the stock, livers, capers, vinegar, and lemon juice. Add the reserved guinea thighs and bring the braise to a simmer. There should be well more liquid than is needed to cover the meat. This is a good thing, as this dish is all about having plenty of sauce and it will reduce as you cook it. Simmer until the guinea is fork-tender and the meat pulls away from the bone easily, 1 to 1 1/2 hours. Carefully remove the thighs and reserve on a plate.
6) Turn up the heat and boil the sauce, stirring from time to time to make sure it isn't sticking and burning, until it reduces by half. To thicken it slightly, use a blender to puree 1 cup of the reduced sauce and add it back to the pan. Stir and taste for seasoning. Add a couple drops of lemon juice if needed. Salt is probably not needed, but use your judgment for final seasoning.
The dish can be made up to this point a day ahead.
To finish, preheat the oven to 400 degrees F.
7) Put the bread slices in a small baking dish that has been generously coated with olive oil. Ladle the remaining 1 cup of stock evenly over all of the bread. Set two thighs on each slice, skin side up. Toast in the oven until the bread has turned a crispy golden brown on the bottom, about 10 minutes; use a spatula to check and be careful as the toast tends to stick. Reheat the sauce.
8) Remove the thighs from the toasts, and carefully remove the crostones from the pan and turn them over so that the brown side is up.
9) To plate, set one slice of toast on each plate. Remove the thigh bone from the meat and place the meat from two thighs on each toast. Spoon some of the warmed sauce over each thigh and a little more to run off the crostone. Garnish with celery leaf (inner yellow leaves only), Italian parsley leaf, and long strips of lemon zest.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.