Lamb loin with vinegar-cooked potatoes and anchovy dressing

By Matt Tebbutt From Saturday Kitchen Ingredients For the lamb 1 lamb loin 15g/½oz butter 1 garlic clove, smashed few thyme sprigs 25ml/1fl oz Madeira salt and freshly ground black pepper For the potatoes 250ml/9fl oz cider vinegar 10 baby potatoes, peeled 1–2 tbsp salt 100g/3½oz …