Remove the skin and tendons from the leg of venison, then clean the meat.
Mix the salt, pepper, hot paprika, thyme, and rosemary into the buttermilk. Add the minced garlic and stir well.
Place the meat and marinade in a freezer bag, seal tightly, and refrigerate for at least 8 hours or overnight.
Heat the clarified butter in a large roasting pan over medium-high heat. Sear the meat on all sides until browned (about 5–8 minutes total).
Add the remaining marinade, coarsely chopped onion, game stock, and roughly 100 ml water to the pan. Arrange sliced bacon over the meat. Cover the pan with a lid.
Place the covered roasting pan in a preheated convection oven at 140 °C (284 °F) and roast for 2 hours 30 minutes.
Remove the meat from the pan and let it rest for 20 minutes. Strain the pan contents through a fine sieve to make a sauce. Season to taste or thicken with a roux if desired.