Preheat oven to 160°C (320°F).
Take a large glass bowl, and add the braising/stewing beef, flour, salt and pepper and mix them thoroughly so that the beef is coated with other ingredients.
Place a large Dutch oven pot (or large casserole pan) on induction stovetop, add 2 1/2 tbsp of vegetable oil and heat up. Cook the beef on medium heat untill it turns brown in 4-5 minutes (Remember that you may need to do this in 2-3 batches depending on the quantity of beef and number of servings).
When the beef turns brown, add the onion in the same pan and again cook on a low heat until the onions start to soften. This may take 3-4 minutes.
Now, add in the garlic, celery, and carrot, cook for another two minutes. Stir frequently to cook veggies properly. At this stage, you can add the optional ingredients like bell pepper, mushrooms and zucchini.
When the veggies have cooked, add the tomato paste/puree and stir. Once it mixes with veggies and beef, then add in the wine, and turn up the heat. Stir for another couple of minutes until wine bubbles. Make sure the ingredients don't stick at the bottom of pan by stirring continuously, otherwise, the beef and veggies may burn.
Now, it's time to add the beef stock, chopped tomatoes, and dried thyme and (optional) oregano. Stir everything together, and bring it to the boil by placing a lid on the pan for a few minutes.
Now place this pan into the preheated oven for 3-4 hours untill the beef is lovely and tender. Here the trick is to check the sauce every hour to make sure it doesn't dry. If the sauce looks dry, top up with a splash of boiling water or stock.
Once the beef is tender and cooked properly, remove from the oven.
You can serve beef ragu with with rigatoni pasta, pappardelle. pasta or any of your favorite. Although I recommend serving the sauce on top of the pasta, you can also stir the rigatoni through the sauce. Top with a sprinkle of cheese and parsley, then serve.