Preheat oven to 180 degrees C. Grease a large casserole dish.
Peel and cut potatoes into thin slices and place in a bowl of cold water.
Heat the oil in a frying pan and add mince, onion, sauces, salt and pepper. Cook over a medium heat until the mince is browned.
To make the cheese sauce: melt the butter in a medium saucepan. Add the flour, blend until smooth and gradually add the milk and stir until sauce thickens. Reduce the heat to low and stir in cheese. Season to taste and remove from heat.
Line a casserole dish with half the drained potato slices. Pour in the mince mixture and top with mushrooms. Pour the cheese sauce over the mince mixture and top with remaining potatoes. Dot the potatoes with extra butter.
Cook for 30-40 minutes till the top is browned and bubbling.