If your roasting tin is flame-proof, put it on a medium heat, otherwise scrape everything into a saucepan, making sure you get all the sticky bits on the bottom, and put on a medium heat. Scatter over the flour, stir it into the sticky veg to make a paste and cook until it turns light brown. Pour in the wine and bubble down until sludgy, then pour over 1.5 litres water and add or crumble in the stock. Bring to the boil, stirring well and scraping the bottom of the pan, then lower the heat and simmer gently for 30 mins until you have a lightly thickened gravy.