Slow cooker corned beef with horseradish sauce

Ingredients

• SLOW COOKER CORNED BEEF
• 1.5kg piece corned silverside
• 1 medium brown onion (150g), chopped coarsely
• 1 medium carrot (120g), chopped coarsely
• 1 stalk celery (150g), trimmed, chopped coarsely
• 10 black peppercorns
• 1 tablespoon brown malt vinegar
• 1 teaspoon brown sugar
• 2.5 litres (10 cups) water, approximate
• HORSERADISH SAUCE
• 2 cups (500ml) milk
• 45g butter
• 2 tablespoons plain (all-purpose) flour
• 1 tablespoon horseradish cream
• 1 tablespoon fresh flat-leaf parsley, chopped coarsely