Beef Stew With Onions, Tomatoes, and Mushrooms

3 lbs beef stew meat , preferably chuck, trimmed of excess fat kosher salt fresh ground pepper vegetable oil 2 tablespoons butter 3 yellow onions , thinly[...]

1/4 cup olive oil 3 lbs beef chuck , cut into 1-inch cubes 3 cups chopped onions 2 garlic cloves , minced 1 cup dry red wine 8 cups beef broth 3/4 cup diced[...]