Working in batches as necessary, add cooking oil and venison to a large skillet over medium-high heat and sear venison on all sides until a brown crust forms. Remove from skillet and set aside.
Add additional oil if needed and saute the onions and mushrooms in the skillet until tender and onions begin to brown. Add minced garlic and cook for an additional 2 minutes, or until fragrant.
Remove onions, mushrooms, and garlic from the skillet and deglaze with 1/2 cup of beef stock. Whisk and scrape the bottom of the pan to incorporate all of the burnt on fond into the liquid. Pour off and reserve deglazing liquid with venison and vegetables.
Melt butter in a soup pot or Dutch oven over low heat and sprinkle in flour to form a roux. Whisk continually for 5 minutes, to prevent scorching, or until roux turns from blond to a light brown.
Slowly incorporate beef stock into the roux, mixing to combine as it is added.
Add venison, mushrooms, onions, and garlic to the soup pot along with the reserved deglazing liquid, tomato paste, Worcestershire sauce, bay leaves, one sprig of sage, and fresh ground pepper.
Cover the pot and let simmer for two hours. 10 minutes before serving, add an addition sprig of fresh sage and taste for salt, adjusting as needed.
Serve with hot dinner rolls.