Slow Cooker Beef Stroganoff

For the Stroganoff:
1 1/2 pounds bottom round roast or chuck roast, cut into 2-inch chunks
2 teaspoons salt
1 teaspoon black pepper
1 teaspoon garlic powder
3 tablespoons all-purpose flour
2 tablespoons vegetable oil
3 cloves garlic, crushed
1 medium white onion, diced
8 ounces cremini mushrooms, sliced
3 cups beef broth
1 tablespoon Dijon mustard
1 tablespoon Worcestershire sauce
1 bay leaf
To finish:
12 ounces egg noodles
1 1/2 cups sour cream
1 cup beef broth (optional, if needed)
1 tablespoon fresh dill, chopped
1 tablespoon fresh parsley, chopped