Crockpot Beef Bites and Gravy

Ingredients:

3-4 pounds beef stew meat, cut into 1-inch pieces

1 (14.5 ounce) can beef broth

1 (0.87 ounce) packet brown gravy mix

1 (1 ounce) packet au jus mix

1 large onion, chopped

1/2 stick (4 tablespoons) unsalted butter

2 tablespoons minced garlic

1 cup sliced mushrooms (optional)

Salt and black pepper, to taste