Ingredients: 500g pink fir or charlotte (or other waxy) potatoes 75ml olive oil 1 small onion, finely chopped (125g) 1 garlic clove, crushed 175ml chicken stock 2 tsp Dijon mustard 2 tbsp apple cider vinegar ½ tsp black peppercorns, coarsely crushed 15g chives: 10g finely chopped…