Beef ,Onion and Mushroom Casserole

This casserole is great for those cold days and very tasty. I make double the quantity and freeze for later use.
Ingredients
2 cups--550 gm--1 lb stewing beef, braising steak or rump steak. These are the names for it in the UK. I cut it into chunks and remove the fat. I keep some fat to add to the flavour and any veins of fat will melt away during cooking.
2 large onions chopped
2 cups--200 gm--8 oz--sliced or chopped mushrooms
1 oxo cube or 1 beef stock cube
2 cloves of garlic chopped very fine
1 teaspoon of tarragon
water to cover, about 1/2 pint--250 ml
salt and pepper
1 teaspoon of cornflour
Method
Place meat, onions, garlic, mushrooms, salt, pepper and tarragon into a casserole dish. Crumble the stock cube over the ingredients and then add water. I then cover the casserole dish with foil and place the lid on the top.
I cook it at gas 5, 190C, 375 F for 2 1/2 hours. I check after 1 hour to see if it needs any extra water. At the end of cooking put the cornflour into a cup, add 2 teaspoons of water, stir until it is smooth and add to the casserole, stir well and it will thicken the gravy.
Serve with baked potatoes and a green vegetable.
Variations
1. Use lager , beer, stout or Guinness instead of water, this makes it really tasty.
2. Use mixed herbs, thyme, oregano instead of tarragon. I expect you will have a personal preference but I love tarragon.
3. You can fry the meat in a pan with some olive oil and then put it into the casserole, this will seal in the juices and add to the flavour. If you toss the meat in flour prior to frying it will then thicken the casserole.
4. Omit the garlic if it is not to your taste.