Put everything (except the poultry, obviously) into a blender and puree until smooth—it helps to start on a slow setting, working your way up, and let it blend for a minute or so once it’s all combined to make sure everything is minced. Set aside.
Remove the backbone from the turkey/chickens with kitchen shears. Open the bird up and cut through the cartilage right between the two breasts up towards (what was) the neck area. Open the bird up with the skin facing upwards and with the heel of your palm press on the breast, in the middle towards the top, to break the breastbone.
Pour about a third of the marinade into a separate dish and set aside.
Take the remaining marinade and spread over the underside of the bird and underneath the skin, right onto the meat. I gently slide my fingers between the meat and skin and then spoon the marinade in, gently massaging the skin to spread the marinade over the meat. Spread whatever remains over the skin itself.
Set the bird(s) of choice on a wire wrack in a roasting tray and marinade, uncovered, in the fridge for 24 hours (give or take an hour or two).
Let the turkey come to room temperature for 2 hours before you start cooking.
Preheat the oven to 450°.
Pour 1 ½ cups of the stock in the bottom of the pan. This serves two purposes, one being for basting, but also—and perhaps more importantly—prevents any drippings from burning in the pan as they fall from the bird.
Roast in the preheated oven—50 to 70 minutes for a turkey, 40 to 50 minutes for the chickens, or until they register 160° on a digital thermometer in the thickest part of the breast. Baste it every so often, particularly the breast, taking care not to keep the oven door open too long.
For the gravy, reduce the Marsala in a saucepan over medium-low until you’re left with nothing but about 2 tablespoons of thick, syrupy liquid—about 15 – 20 minutes. Pour in the remaining stock and bring to a boil. If you’re stock is boiling before the bird is done just cover it and keep over low heat to stay warm.
When the turkey is done roasting remove it from the oven and lightly tent it with foil to keep warm and carry-over cook for about 10 minutes.
Meanwhile, bring the stock back to a boil. Put the flour into a liquid measuring cup. Set a fine mesh sieve over it and pour some of the liquid from the bottom of the pan through the sieve and into the cup. Whisk to combine, adding more liquid until you have a smooth, pourable slurry.
Pour the slurry into the boiling stock, whisking it vigorously to combine. Let it boil for another minute or two before reducing the heat to lower, simmering until thick.
Decant the gravy into a gravy boat and carve the turkey.
If you need a good Turkey Stock recipe look no further that HERE.