1-First Step: Cook the bacon Start by placing 200 g (6 oz) streaky bacon, chopped into a cold non-stick pan. Turn the heat to medium and cook it without oil. This method helps the fat render slowly, so the bacon turns golden and crisp instead of greasy and sad. Once cooked, drain it on paper towels and set it aside.

2-Second Step: Prep the potatoes Peel the 1.75 kg (3.5 lb) potatoes and cut them into even 3 cm chunks. Keeping the pieces the same size matters because it helps them cook at the same pace. If some chunks are huge and others are tiny, you will end up with a weird mix of mush and firmness, which nobody invited.

3-Third Step: Boil until very soft Place the potatoes in a large pot and cover them with cold water by about 10 cm. Add 1 tablespoon kosher or cooking salt. Bring the pot to a boil, then lower the heat and simmer rapidly for about 15 minutes, or until the potatoes are very soft and easily pierced with a fork. This is the moment that sets up the creamy texture for your cheesy mashed potatoes.

Once they are done, drain the potatoes very well and return them to the pot. Shake the pot gently every so often for about 1 minute. That little trick helps steam escape so your mash does not become watery.

4-Fourth Step: Mash with the creamy mix Add the 75 g (5 tablespoons) unsalted butter, 2/3 cup milk, 1/2 cup sour cream or full-fat yogurt, and 1 teaspoon salt, or to taste. If you are making the make-ahead version, add the extra 2/3 cup milk now too. Mash everything until smooth and fluffy.

5-Fifth Step: Assemble the casserole Spoon the mashed potatoes into a 2-liter (2-quart) baking dish and spread them evenly. If you only have a 3-liter dish, that works too, though the casserole will look a little less full. Sprinkle the top with 1 1/2 cups freshly shredded mozzarella and 1 cup freshly shredded Red Leicester, cheddar, or other flavored cheese. Then add the cooked bacon over the top.

6-Sixth Step: Make it ahead if needed For a make-ahead easy cheesy potato casserole, cover the dish with cling wrap and refrigerate it for up to 3 days. Take it out about 2 hours before baking so it has time to come closer to room temperature. That helps it heat through evenly instead of staying cold in the middle.

7-Seventh Step: Bake until bubbly Preheat the oven to 200°C (400°F) or 180°C fan. Cover the dish loosely with foil and bake for 20 minutes if it is freshly made, or 35 minutes if it is coming from the fridge. Then remove the foil and bake for another 10 minutes until the cheese is bubbly and golden on top.

8-Final Step: Finish and serve Sprinkle with 1/4 cup finely sliced green onion just before serving. The green onion gives a fresh little pop that cuts through the richness nicely. Serve warm and let everyone dig in while the cheese is still stretchy and the bacon is still crisp.