In a bowl, combine the ground venison, crushed croutons, Dijon mustard, egg, parsley and salt. Using your hands, mix the ingredients together and form 12 meatballs of equal size. Set aside when done.
Heat a skillet over medium heat and add 2 tablespoons butter and the extra virgin olive oil. Add the shiitake mushrooms, onions and remaining garlic. Cook until the onions are caramelized and browned, about 8-10 minutes. Remove the mushrooms and onions from the skillet and set aside.
Add the venison meatballs to the skillet and brown, about 8-10 minutes. Remove the meatballs when done and set aside.
Add the remaining butter and flour to the skillet stirring to form a paste. Continue stirring while slowly adding the beef broth creating a thin smooth gravy. Reduce the heat to low and continue stirring until gravy begins to thicken.
Add the meatballs to the skillet along with the mushroom and onion mixture. Continue to cook for 8-10 minutes until done.
Season with salt and pepper to taste and garnish with fresh parsley.