1 iceberg lettuce
½ red onion, finely diced
salt and freshly ground black pepper
½ tsp mustard powder
1 tsp olive oil
salt
pinch sugar, plus extra to taste
1 tbsp cider vinegar
1 tbsp cider vinegar, plus extra to taste
100ml/3½fl oz buttermilk
75g/2¾oz soft blue cheese, such as gorgonzola
50ml/2fl oz soured cream
6 rashers rindless streaky bacon