In a large skillet or Dutch oven, heat the olive oil over medium heat. Add the sausages and cook until browned on all sides, about 5-7 minutes. Remove the sausages from the skillet and set aside.
In the same skillet, add the butter and sliced onions. Sauté until the onions are soft and translucent, approximately 5 minutes.
Sprinkle the all-purpose flour over the onions and stir well to combine. This will help to thicken your casserole. Cook for an additional 2 minutes to remove the raw flour taste.
Gradually whisk in the beef broth and water, ensuring there are no lumps. Add the Worcestershire sauce and barbecue sauce and stir to incorporate.
Sprinkle in the dried herbs (sage, parsley, thyme, and rosemary) along with salt and pepper to taste. Stir well.
Return the browned sausages to the skillet, nestling them into the sauce. Bring the mixture to a gentle simmer.
Cover the skillet and let the casserole simmer for about 20-25 minutes, allowing the flavors to meld and the sausages to cook through. Stir occasionally. Once ready, serve hot and enjoy!
