This is the ultimate steak sandwich recipe - Better Homes & Gardens Australia

Ingredients

• 300ml water
• 200ml white wine vinegar
• 1 Tbsp coriander seeds
• 1 bay leaf
• 1/2 Tbsp caster sugar
• Sea-salt flakes and freshly ground cracked black pepper, to season
• 150g shimeji mushrooms, ripped
• 150g oyster mushrooms, ripped
• 375g portobello mushrooms, finely sliced
• 1kg piece hanger or flank steak, sliced in half lengthways
• Mustard sauce
• 200g whole egg mayonnaise
• 1 tsp onion powder
• 1 tsp garlic powder
• 1 tsp dijon mustard
• 1 tsp ketchup (tomato sauce)
• Pinch cayenne pepper
• 1 Tbsp lime juice
• 2 tsp white wine vinegar
• Caramelised onions
• 2 Tbsp olive oil
• 4 large brown onions, finely sliced
• 1–2 Tbsp sherry or red wine vinegar
• 8 thick slices sourdough bread
• 3 large oxheart tomatoes, thickly sliced