Spray a frying pan with low-calorie cooking spray and set on a medium heat. Add the onion, peppers, garlic, and carrot, and gently fry for 8-10 minutes.
Add the beef to your pan, then fry for 4-5 minutes – until browned.
Pour in the chopped tomatoes, passata, tomato puree, Henderson's relish, stock cube, and mixed herbs. Stir well, and simmer for 15 minutes – until thick and reduced. Bear in mind you don't want the bolognese to be too wet when you add your mixture to the puff pastry.
Leave your bolognese mixture to cool. Preheat the oven to 200ºC, and line a baking tray with non-stick baking paper.
Unroll the pastry sheet, leaving it on the greaseproof paper packing, and place it on a work surface. Then spread the bolognese mixture over the pastry sheet in an even layer – leaving a 1cm gap along one long edge.
Roll up the pastry tightly – starting with the long edge without the 1cm gap, and using the greaseproof paper to help you. Keep rolling the pastry up until you have a "Swiss roll". When you've finished rolling the pastry, make sure it's seam-side down, then use a large, serrated knife to cut it into 16 spiral-shaped slices.
Transfer the slices to your lined baking tray – leaving gaps between each one. Press the seam on each to ensure a good seal.
Brush your pastry with the milk and sprinkle over the cheese, then bake in the oven for 15-20 minutes – until golden brown and crisp.