Heat the butter and oil in a large sauté pan with a lid until sizzling.
Add the onion, carrots, celery, garlic, mushrooms and bacon and sauté over a medium heat for 10 minutes until the vegetables have softened and everything is lightly browned, stirring frequently.
Add the minced beef to the pan, reduce the heat and cook gently for 10 minutes until well browned, stirring to break up any lumps with a wooden spoon.
Stir in the tomato puree, canned tomatoes and half of the stock and bring to the boil, stirring to combine.
Reduce the heat under the pan, half cover with the lid and simmer very gently for about 2 hours or until the meat is meltingly tender, stirring occasionally and adding a little more of the remaining stock as it becomes absorbed.
Add basil to the sauce and mix well to combine, then simmer uncovered for another 30 minutes until the bolognese sauce is well reduced and thickened, stirring frequently.