Best Beef Stroganoff

Name: Best Beef Stroganoff
Prep time: 10 min
Cook time: 20 min
Total time: 30 min
Cuisine: Eastern European
Ingredients: 1 tbsp oil; 1 tbsp butter; 1 onion (thinly sliced); 225g/1/2 lbs crimini mushrooms/chestnut mushrooms (sliced); 450g/1 lbs beef steak (I used sirloin) (cut in strips); 60ml/1/4cup brandy; salt; pepper (freshly ground); 125ml/1/2 cup beef stock; 1 bay leaf; 1 tsp whole grain mustard; 250ml/1 cup full fat creme fraiche or sour cream; 3-4 sprigs-flat-leaf parsley (chopped)