In a hot pan, sauté the vegetables and pancetta in two tablespoons of olive oil over a low heat until the onions are translucent. Season with a pinch of salt and the thyme.
Then increase the temperature and add the mince to the mixture in the pan. Stir-fry until the meat is well browned. Break up larger lumps of meat with the back of a spoon.
When the meat is browned, season with salt and pepper and deglaze with the white wine. Season with salt and pepper and stir well. Reduce the heat, add the vegetable stock and simmer the ragù for 10-15 minutes. Then stir in the cold butter to thicken the sauce.