Sausages with creamy mustard sauce

Name: Sausages with creamy mustard sauce
Ingredients: 300g/10½oz new potatoes, quartered; 3 tsp sunflower oil; 2 medium carrots (around 150g/5½oz), peeled and cut into batons; 1 medium parsnip (around 125g/4½oz), peeled and cut into batons; ½ medium onion, cut into 8 wedges; 1 medium courgette (around 175g/6oz), halved lengthways and cut into 1.5cm/⅝in chunks; 4 good-quality sausages; sea salt and freshly ground black pepper; cooked green vegetables, such as shredded cabbage or kale, to serve; 100ml/3½fl oz apple juice or cider; 1 tsp wholegrain mustard; 1 tsp Dijon mustard; 4 tbsp double cream