Beef Stroganoff Cottage Pie with Crispy Parmesan

Ingredients

• 2 cups beef broth ((500 ml))
• 2 tablespoons unsalted butter ((40 g))
• 1 tablespoon sweet paprika
• 1 large onion, diced
• 2 tablespoons all-purpose flour
• 1 tablespoon Dijon mustard
• 1 teaspoon minced garlic
• 1/2 cup grated Parmesan cheese ((50 g) fresh)
• 14 oz sliced mushrooms ((400 g))
• 1 tablespoon Worcestershire sauce
• 1 3/4 lbs beef chuck, cut into bite-sized cubes ((800 g))
• 2 tablespoons olive oil
• 1/2 teaspoon black pepper (cracked)
• 1 teaspoon salt
• 2 tablespoons sour cream
• 2 tablespoons tomato paste
• 2 1/2 lbs potatoes, peeled and quartered ((1.2 kg))
• Olive oil spray
• 1 cup milk, warmed ((250 ml))