Place mushrooms, in a small heatproof bowl and add enough boiling water to just cover. Set aside for 10 mins to rehydrate.
In a food processor in batches, finely mince (but don't puree) carrots, then celery and leek, then zucchini and mushroom (and liquid). Set these all aside in one bowl.
Process the tomatoes until smooth and set aside.
Heat the oil in a large, heavy based pot and fry mince for 10-15 mins, or until all the liquid has evaporated and you are left with a layer of "brownings" (not burnings though!) in the bottom of the pot.
Add rosemary, thyme and garlic. Cook for 1-2 mins until garlic is fragrant but not browned.
Add the chopped bacon & vegetable mixture and cook, stirring occasionally for 15-20 mins or until vegetables have softened, the liquid has evaporated and a new layer is formed on the bottom.
As they cook they vegetables will release moisture which will deglaze the bottom of the pot, releasing all the flavour from the brownings into your sauce. Make sure to scrape the bottom of the pot as this happens, this allows a new layer of brownings to develop.
Reduce heat to low, add 1 1/2 cups of milk to again deglaze the pan (scraping as you go) and cook for 10-15 mins or until milk has evaporated and you have another layer at the bottom.
Repeat with the remaining milk.
Add tomatoes, beef stock and vinegar to again deglaze the bottom of the pot and simmer for 30 mins, or until sauce thickens and deepens in colour.
Serve with pasta and parmesan.