Easy beef stroganoff | Lamb and Beef

Ingredients

• 600 g beef spips
• 30 g butter
• 1 small onion, chopped
• 250 g mushrooms, thinly sliced
• 0.75 cup beef stock
• 2 tbsp tomato paste
• 250 ml carton of light sour cream
• 1 tsp cornflour
• egg noodles to serve