Remove silver skin from venison loin. Cut venison loin in half and place into a container with whole milk, garlic cloves, black peppercorns and rosemary. Cover container and refrigerate overnight.
To prepare the raspberry sauce, combine raspberry preserves and water in a small saucepan and place it over medium-high heat. Swirl in the butter and cook until it’s slightly thickened and reduced, about 5 minutes. Turn heat off and cover pan to keep sauce warm.
Drain milk from venison, pat venison dry with paper toweling and discard all other ingredients.
Place the bacon strips on a cutting board, forming two large bacon sheets. Place one half of venison on one of the bacon sheets and gently roll it, covering venison in bacon. Repeat the process with the other half of the loin. Season the bacon-wrapped loins with salt and pepper.
Place a large cast-iron skillet seasoned with oil on a stove top over medium-high heat. Place the loin halves in the hot skillet, seam side down. Sear for 4 to 5 minutes, until the bacon becomes crispy. Turn over and sear the other side for same amount of time. With a pair of tongs, continue to turn the venison to sear all sides, so the bacon is crispy on all sides. Cook the meat to medium-rare.
Remove venison from pan and allow to rest on a cutting board for 2-3 minutes, then slice venison into medallions and transfer to serving platter. Drizzle raspberry sauce over venison before serving.