1Place dried chillies in a large bowl, cover with 2 cups boiling water. Set aside for 20 minutes, until the chillies are plump. Drain, reserving the liquid. Discard the chilli stems and finely chop chillies.
2Fry bacon in a large frying pan over a medium heat for 5 minutes, until golden. Add beef mince, increase the heat to high, and cook for 8 minutes until well-browned.
3Finely chop half the mushrooms, and cut the remainder into quarters. Add the chopped mushrooms to the mince and cook for 4 minutes, then set aside.
4Put fennel, cumin seeds and olive oil in a deep frying pan over medium heat, cook 3-5 minutes until aromatic. Add onion, garlic and oregano and cook for 4 minutes, until softened. Add to the meat mixture, with the quartered mushrooms. Scatter with flour, then cook until the mixture begins to stick to the bottom of the saucepan. Pour in the reserved chilli liquid and stock, season with salt and pepper, then simmer for 2 hours, topping up with water as needed, until the mixture is very tender and the sauce is thickened.
5Serve with salsa, guacamole, sour cream and tortillas.