Preheat oven to 350 degrees F (175 degrees C).

Heat vegetable oil in a Dutch oven or heavy pot over medium-high heat.

Fry the sirloin tip roast in hot oil until browned on both sides, about 10 minutes.

Pour drained mushroom stems and pieces and 1 cup of beef broth over the roast.

Sprinkle the onion soup mix over the roast and mushrooms.

Bake in preheated oven for about 90 minutes, or until an internal temperature of 145 degrees F (65 degrees C) for medium doneness.

Remove roast from Dutch oven to a platter.

Cover the roast with a doubled sheet of aluminum foil.

Allow the roast to rest in a warm area for 10 to 15 minutes before slicing.

Whisk cornstarch and the remaining 1/4 cup of beef broth in a bowl.

Stir the cornstarch mixture into the Dutch oven with mushrooms and pan drippings.

Bring to a boil over medium-high heat.

Cook and stir until the gravy is thickened, about 2 minutes.

Serve the gravy over sliced beef.