2 garlic cloves, bashed
1 leek, thinly sliced
2 thyme sprigs, plus extra to garnish
900g/2lb waxy potatoes, scrubbed or peeled and thinly sliced (ideally on a mandolin)
3 bay leaves, plus extra to garnish
salt and freshly ground black pepper
butter, for greasing
400ml/14fl oz double cream
50g/1¾oz Gruyère, grated
600ml/20fl oz semi-skimmed milk
50g/1¾oz Parmesan, finely grated
6–8 rashers dry-cured, smoked streaky bacon, snipped into small pieces with scissors (optional)