The Perfect Steak Sandwich

Ingredients

• 1 tablespoon olive oil
• 1 large onion, thinly sliced
• 1 tablespoon each brown sugar and balsamic vinegar
• 2 tablespoons good quality mayonnaise
• 1 teaspoon lemon juice
• 1/4 clove crushed garlic
• 2 teaspoons chopped parsley
• 4 x 150g scotch fillet steaks
• salt
• freshly ground black pepper
• 8 thick slices sourdough bread, lightly toasted
• 40g dressed rocket leaves
• 2 tomatoes, thickly sliced
• 4 rindless rashers bacon, cooked until crisp
• 125g vintage cheddar, sliced
• French fries, to serve