Preheat the oven to 325°F (160°C or 150°C for fan ovens).
Heat 1 tablespoon of the oil or butter over medium heat in a large lidded casserole that will go from the stove to the oven (or use a large frying pan for the stove top part and then transfer the mixture to a casserole before putting it in the oven).
Gently fry the onion in the oil or melted butter, stirring often. Sprinkle with a bit of salt to prevent it browning to quickly. You just want the onion to soften.
Add the remaining oil or butter to the pan and when it has melted in, add the cubed pieces of meat. Brown the meat gently, turning it so that the red colour disappears on all sides.
Lower the heat and sprinkle the meat and onions with the flour.
Stir in the flour and cook for a moment or two.
Stir in the ale, followed by ¾ cup of the beef stock. Reserve the remaining ¼ cup of beef stock.
Cook for a moment or two.
If you are using a frying pan transfer the mixture very carefully to an oven safe casserole now. Be careful not to burn yourself.
Stir in the carrots, along with a good grinding of pepper.
Tuck the bay leaf in under the liquid, cover the casserole and put it in the oven. Set the timer for half an hour.
When the timer goes off, carefully remove the casserole from the oven.
Remove the lid and stir. There should be a good amount of liquid in the pan at this point. If not, add some of the remaining stock.
Cover the casserole and return it to the oven for an hour.
Remove the casserole from the oven once again.
Remove the bay leaf, being careful not to burn yourself.
Take a spoonful of the gravy and place it in a little bowl to cool.
Meanwhile, check the thickness of the gravy. If it has not thickened up, mix a tablespoon of cornflour (corn starch) with 1 tablespoon of water and then stir it into the casserole. If it is too thick (this is unlikely but it does happen sometimes), add the remaining stock.
Taste the spoonful of gravy you set aside earlier, being careful as it still may be hot. Add salt and pepper to the casserole to taste.
Cover the casserole and return it to the oven for about fifteen minutes or up to half an hour.
Remove the casserole from the oven and allow it to rest with the lid on for 15 to 20 minutes.
Serve the Beef and Ale Stew garnished with the parley.