Combine gin, port, thyme and juniper berries in a medium shallow baking dish. Add the venison and turn to coat. Cover and marinate in refrigerator for 30 minutes. Heat oil in a large saute pan over high heat until almost smoking. Remove the venison from the marinade and shake off excess. Season with salt and pepper to taste. Cook on one side until golden brown. Turn over, reduce heat to medium and continue cooking until medium-rare, 3 to 4 minutes.

Heat butter in a medium saucepan over medium-high heat. Add the onions, celery and carrots and cook until soft. Raise the heat to high and add the port, cook until dry. Add the spices, cranberry juice, and chicken stock. Strain the sauce and discard solids. Return to pan to heat, whisk in the cold butter, stir in cranberries, and heat through. Season with salt and pepper to taste.

In a bowl mash potatoes with rest of ingredients.