Preheat the oven to 350 degrees.
Boil water for the potatoes and add them to the pot. Boil for 10-12 minutes or until the potatoes are soft enough to easily pierce with a fork.
Add olive oil to a large pan and when it's heated through add in the onions, garlic, carrots and celery. Cook for 4 minutes or until the onions start to become translucent.
Add in the beef and begin to brown it.
Once browned, add in the tomato paste, Worcestershire sauce and beef broth. Combine well and simmer for 5 minutes.
Add in the peas, corn and the herbs. Simmer for another 5 minutes.
Once the potatoes are done, drain them and then add them back to the pot with the other ingredients for the potatoes (except the onions). Use a potato masher until they are smooth and creamy. Then stir in the onions.
Add the beef mixture to an oven safe baking dish and then layer the potatoes on top of that.
Add on cheese if you like and then bake for 25 minutes.
When done, sprinkle with additional thyme and serve.