Preheat the oven to 190°. Heat a large saute pan over medium heat and add 1 tablespoon olive oil. Add the pancetta to the hot oil and render its fat. Once it begins to brown, add the ground pork and prosciutto and cook, while stirring, about 4 minutes. When the pork is no longer pink, add the garlic and sage and saute until fragrant, about 1 minute more. Deglaze the pan with 1/4 cup white wine, scraping up the browned bits from the bottom of the pan. Stir in the bread crumbs. Remove the stuffing mixture to a bowl and allow to cool.
Season the cavity of the birds with salt and pepper. Divide the stuffing evenly between the two pheasants' cavities. Roast the pheasants 25 minutes. Add 1/2 cup white wine to the bottom of the pan. Turn the oven heat up to 220°C and cook another 25 minutes, or until a thermometer inserted in the thickest part of breast registers 71°C Allow to rest 10 minutes before serving so the juices can redistribute. Remove the dressing from the bird and serve along side. Garnish the dish with fresh sage leaves.