Slow cooker vegetarian hotpot

Name: Slow cooker vegetarian hotpot
Ingredients: 2 tbsp sunflower oil; 1 small butternut squash (approximately 800g/1lb 12oz), scrubbed, deseeded and chopped into chunks; 2 onions, thinly sliced; 3 carrots, peeled and cut into chunks; 2 parsnips, peeled and cut into chunks; 2 tbsp plain flour; 400g tin chopped tomatoes; 2 tbsp tomato purée; ½ tsp dried chilli flakes (optional); 3 tbsp pesto (optional); 350ml/12fl oz hot vegetable stock (made with 1 stock cube); 100g/3½oz young spinach leaves (optional); salt and freshly ground black pepper; 200g/7oz self-raising flour; 75g/2¾oz frozen butter (or 75g/2¾oz shredded vegetarian suet); 125ml/4fl oz cold water