Pre-heat your oven to 180C Fan/400F/Gas Mark 6
Prepare the butternut squash and toss it the oil, then add the sage and stir it in to coat the chunks of squash, then place onto a baking tray and roast for 15 minutes
Meanwhile, cook the diced leek, onion and garlic in a pan on a low heat with a little oil. Cook for 5-8 minutes until the leek and onion are softened. Then set aside to cool
Roll out the puff pastry sheet onto a baking tray, many come with baking paper attached but if not, line your tray first with baking paper
Prick the pastry all over with a fork, avoiding the border of the pastry
Spread the leek out evenly onto the pastry sheet, leaving a 1cm border around the edge
Arrange the butternut squash and stilton over the leek, then glaze the edge with the milk using a pastry brush
Bake the tart for 20-25 minutes until golden all over and the cheese is bubbling
Serve immediately, once fully cool store leftovers in the fridge for 2-3 days or freeze for up to 3 months