Heat some vegetable oil in a big pan to a high heat. Brown the bacon first then add the mince to brown. Remove from the pan and set aside.
Add a splash more oil if necessary. Add the carrots, peppers and leeks and fry for a couple of minutes to add colour. Add the chopped garlic and stir in to the veg. Chuck in a splash of red wine and let it evaporate. Add the beans and stir in.
Return the meat to the pan, add the can of tomatoes and reduce the heat to low. Add the celery, seasoning and the stock cube and simmer for around 15 minutes.
Preheat your oven to 190C and put the potatoes for the mash into boiling water.
Throw in the mushrooms to the sauce and simmer for a further 15 minutes, or until the sauce has a nice rich texture and isn't overly watery.
At this stage your sauce and potatoes should be ready to rock, and your oven pre-heated. As long as you don't kill the mash, then you can relax. There's very little left that can go wrong.
Add the sauce to a suitable ovenproof dish. Mash the potatoes (I prefer very slightly over-boiling them and using only butter instead of milk) and spread evenly over the top of the sauce. I tend to use a fork, which i can then use to make the top nice and fluffy - the sticking up parts will crisp more and it adds to the flavour. Optionally you can add a little grated cheese over the top and a grinding of pepper.
Bake for around 35 minutes, or until the top is golden and crispy. Eat.
This sauce is very versatile and also works great for bolognese, chilli with the addition of some chillis or any other similar dish.