Peel, wash and chop the potatoes. Cook potatoes in boiling salted water for about 20 minutes. Cut bacon crosswise into strips. Heat oil in a pan and fry bacon crisply for about 4 minutes.
Grate cheese separately.
Drain the potatoes. Add sour cream, approx. 1/2 cheddar and milk and mash to puree. Season to taste with salt, pepper and nutmeg and place in a greased casserole dish. Spread the bacon, rest of the cheddar, parmesan and butter in flakes over it and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see
manufacturer) bake for 20-25 minutes.
Clean, wash and cut the spring onions into rings. Halve the avocado, remove the core and remove the flesh from the skin with a spoon. Cut the flesh into cubes. Remove the casserole from the oven and sprinkle with spring onions and diced avocado.