1. Heat your oven to 100°C/Fan 80°C/Gas ¼. Unpack the tortillas and place them in a large square of foil. Lay the tortillas in the foil and wrap it around them to make a loose parcel. Place on the bottom shelf of the oven to gently warm.
2. If you're using any chunky veg, like carrot batons or whole Brussels sprouts, roughly chop them so all the veg are roughly the same size. Place a medium-sized pan on a medium heat and add 1 tbsp butter. Add the veg and gently fry, stirring often, for 4-5 mins till the veg have warmed through. You shouldn't need to season them, as they'll already be seasoned, but taste and check in case they do need extra salt and pepper. Scoop the veg into a heatproof dish, cover with foil and place in the oven to keep warm.
3. Roughly chop the turkey. Scoop it into the pan you reheated the veg in and add around 150ml gravy – enough to just cover the turkey. Set on a medium heat and reheat for 4-5 mins, stirring occasionally, till the turkey is piping hot all the way through and the gravy has reduced to coat the turkey. Scoop into a heatproof dish, cover with foil and pop in the oven to keep warm.
4. Roughly chop the roast potatoes and/or parsnips to make small chunks around ½cm across. Wipe the pan clean and place it back on a medium heat. Add 1-2 tbsp oil and, when it's hot, add the chopped roasties and fry, stirring, for 3-4 mins, till they're warmed through and a little crisp. Scoop into a heatproof bowl and place in the oven to keep warm.
5. If you have leftover Yorkshire puddings, slice them into thin strips. If you have any cooked stuffing, chop it into small chunks (unless it's soft and can be easily spooned into the burrito). Pour around 400-500ml gravy into the pan and set on a medium-low heat to slowly warm while you're assembling the burritos. You want it to come to the boil, then turn the heat down so it stays steaming hot.
6. Take the flour tortillas, veg, turkey and roasties out of the oven, but leave the oven on. Place 1 tortilla on your work surface. Spread 1 tbsp bread sauce (if using), then 1 tbsp cranberry sauce down the middle of the tortilla. Top with a handful of the roasties, then the veg and then the turkey, making sure it forms a strip down the middle of the tortilla, leaving a gap at the sides. Top with a few strips of Yorkshire pudding and some stuffing.
7. Using both hands, fold the sides in over the filling, then use your thumbs to pull the bottom of the tortilla up and over the filling to create a pouch. Fold the top corners of the tortilla over the filling, so you have something that looks quite square. Roll the burrito to enclose the filling. Transfer to a heatproof plate, seam-side-down, and place on the bottom shelf of the oven to keep warm. Repeat with the remaining tortillas and fillings.
8. To serve, pour the hot gravy into small serving bowls and halve the burritos. Serve them with the gravy for dunking.