Beef cheek and whole mushroom stroganoff

Ingredients

• 50g butter
• 2 large brown onions, peeled and sliced
• 1 tsp Dijon mustard
• 2 tbsp tomato paste
• 2 tsp sweet paprika
• 1.5kg beef cheeks (around 6)
• ½ cup plain flour
• 1 tbsp vegetable oil
• 250ml white wine
• 500ml beef stock
• 500g small button mushrooms
• 1 tsp salt, plus extra to season
• 250g sour cream
• 1 tbsp finely chopped parsley, to serve