German-Style Crushed Potato Salad with Dill Pickles

Ingredients

• 1.2 kg large floury potatoes, such as sebago, scrubbed
• 4 dill pickles, thinly sliced widthways, plus 100ml pickling liquid
• 70 ml chicken stock (substitute with vegetable stock for vegetarians)
• 2 tbsp white wine vinegar
• ½ Spanish onion, thinly sliced
• ½ garlic clove, finely chopped
• 120 gm sour cream
• 1/3 cup each coarsely chopped dill and flat-leaf parsley, plus extra to serve
• Mustard and horseradish mayonnaise
• 2 egg yolks
• 1 tbsp German-style mustard
• 220 ml olive oil
• 3 tsp jarred grated horseradish