Beef Stroganoff Cottage Pie with Crispy Parmesan Topping

Ingredients

• chuck steak, gravy beef or braising steak , cut into bite-sized pieces
• salt
• cracked black pepper
• olive oil
• large onion, roughly diced
• garlic, freshly minced
• mushrooms, sliced
• plain flour
• tomato paste
• sweet paprika
• Worcestershire sauce
• Dijon mustard
• beef stock
• sour cream
• ⅕ kg all-purpose potatoes, peeled and quartered
• unsalted butter
• milk, slightly warmed
• Olive oil spray
• freshly grated parmesan