1.2kg/2lb 12oz medium potatoes, like Desiree, Maris Piper or Elfe, peeled
2 garlic cloves, thinly sliced
3 large onions, sliced
2 tbsp finely chopped flatleaf parsley, plus extra to serve if you like
2 tbsp fresh thyme leaves, plus extra to serve if you like
salt and freshly ground black pepper
2 tbsp olive oil
50驳/1戮辞锄 butter