Winter vegetable pie

INGREDIENTS

• 2 tbsp olive oil
• 2 onions , sliced
• 1 tbsp flour
• 300g (about 2 large) carrots , cut into small batons
• ½ cauliflower , broken into small florets
• 4 garlic cloves , finely sliced
• 1 rosemary sprig, leaves finely chopped
• 400g can chopped tomatoes
• 200g frozen peas
• 900g potatoes , cut into chunks
• up to 200ml/7fl oz milk