Place bacon in a cold non-stick pan over medium heat (no oil). As the pan heats up the bacon fat will melt. Once you see some melted bacon fat, turn the heat up to medium high and stir for 3 minute or until golden.

Drain on paper towels.

Potatoes - Peel then cut into 3cm /1" chunks.

Boil - Place in a large pot and cover with water so it’s 10cm / 4” above the potatoes. Add 1 tablespoon salt. Bring to a boil over high heat then reduce heat so it’s simmering rapidly. Cook 15 minutes or until potatoes are very soft (jab with fork to test, they should fall apart).

Drain well, then return into pot. Leave for 1 minute, shaking pot every now and then, to encourage evaporation of water.

Mash - Add milk (including EXTRA milk if making-ahead), butter, sour cream and 1 tsp salt. Mash until smooth. (Do not use food processor, blender or beater, makes it gluey!)

Fridge - Allow to fully cool on the counter then cover tightly with cling wrap and refrigerate.

Dechill - Take out onto counter 2 hours prior to reheating.

Preheat oven to 200°C / 400°F (180°C fan).

Spread the potato in a 2 litre / 2 quart baking dish (Note 5). Smooth the surface.

Sprinkle - Sprinkle potato with the cheeses, then bacon.

Bake covered - Cover loosely with foil. Bake for 20 minutes covered (if freshly made) or 35 minutes (make-ahead option).

Bake uncovered - Remove foil then bake a further 10 minutes until the cheese is bubbly and golden.

Serve - Sprinkle with green onion then serve! It stays warm for a good 20 minutes thanks to that protective layer of cheese. Oh, the powers of cheese!