Vegetable Cumberland pie

Ingredients

• 2 large potatoes (400g in total), peeled and quartered
• 150ml skimmed milk
• 1 tablespoon vegetable oil
• 1 small onion (60g), finely chopped
• 1 clove garlic, finely diced (optional)
• ½ small butternut squash (200g), peeled, deseeded and cut into bite-size chunks
• ½ red pepper (80g), deseeded and chopped
• 3 mushrooms (50g), wiped and chopped
• 1 medium courgette (150g), washed and cut into bite-size chunks
• 2 heaped tablespoons plain flour
• 1 teaspoon sweet paprika
• 1 x 210g can butter beans, drained
• Freshly ground black pepper