Warm a little oil in a large frying pan over a medium heat. Add the onion, leeks and garlic and cook and stir for a few minutes until soft. Add mushrooms and cook on low till mushrooms have softened and reduced in size, about 6 to 8 minutes.
Add the broccoli, herbs, spices and stock cube, to vegetables and stir well. Once combined add tomatoes, balsamic vinegar and Worcestershire sauce and simmer.
Brown off the beef in a separate frying pan over a medium-high heat and once browned strain off any excess fat and add the beef to the vegetable mixture. Set aside.
In a saucepan bring the milk to the boil and add cornflour dissolved in 2 tablespoons of water to thicken. Once thick, take of the heat and add the grated Cheddar and stir till Cheddar has melted into the sauce then set to one side.
Place the beef mixture into the base of a casserole dish then pour the cheese sauce on top. Sprinkle over the Parmesan cheese.
Bake in the preheated oven for 40 minutes until piping hot. Remove from the oven, serve and enjoy.
As an alternative, why not layer cooked sliced potatoes on top of the cheese sauce and bake till crispy.