Remove the venison from its bath, patting the pieces dry, and reserve the marinade. In a Dutch oven or other large, ovenproof vessel, saute the pancetta in the olive oil for a few minutes, then remove to a plate lined with paper towels. Add the venison chunks, working in batches, and sear on all sides, adding more oil if necessary. When the meat is done, remove it to the plate with the pancetta and season well with salt and pepper.
With a slotted spoon or tongs, remove the meat to a serving plate. Add the grappa to the braising liquid and reduce over a medium flame for 15 minutes. Strain the sauce through a chinois, pressing down on the solids left in the strainer to extract the maximum juice and flavor. Return the strained sauce to the pan and stir in the butter. Season with salt and pepper and add the remaining 1/2 cup red wine to the sauce. Serve the meat with the sauce poured over and the prune jam on the side.
Yield: 2 1/2 cups