BBC Food - Recipes - Prime topside beef burger

Ingredients

• 1 red onion
• 200ml/7fl oz red wine vinegar
• 80g/3oz caster sugar
• 600g/lb 5oz topside beef, minced (your butcher can do this)
• salt and freshly ground black pepper
• 4 fresh white rolls
• 100g/3½oz sliced gherkin
• 8 slices cooked streaky bacon
• 1 Little Gem lettuce
• 2 free-range egg yolks
• 100ml/3½fl oz vegetable oil
• 25ml/1fl oz white wine vinegar
• 1 tbsp wholegrain mustard
• 800g/1lb 12oz Maris Piper potatoes , peeled and cut into chunky chips
• vegetable oil , for deep fat frying
• 1 bunch of rosemary
• sea salt