Step 1

Put the prepared potatoes and garlic into a very large pan, cover with cold water, add the salt, cover with a lid and bring to the boil over a high heat, then turn down and cook partially covered – just a crack – until very tender.

Step 2

Put a colander over a large bowl or another pan and drain the potatoes, letting the starchy water collect underneath. Do not throw this away: it is precious liquid (see recipe tip).

Step 3

Add the butter to the hot, emptied-out potato pan, and let it start melting, then tip in the drained potatoes and garlic. Dip a measuring cup into the cooking liquid, add about 125ml/4fl oz and mash using your chosen method (see recipe tip). You may want to add more of the cooking liquid. I never add less than 250ml/9fl oz, as I like this to be as smooth and creamy as possible, though I’m aware many people prefer a more solid mash. Stir the Parmesan in by hand and check for seasoning before transferring to a warm bowl.

Step 4

If you are making this in advance, butter a small roasting tin or ovenproof dish, measuring approx. 30x25cm/12x10in, and fill with the mashed potatoes, smoothing down the top. Leave to cool, cover and place in the fridge for up to 3 days.

Step 5

On reheating, remove from the fridge and allow to come to room temperature, which will take an hour or two, depending on the weather.

Step 6

Preheat the oven to 200C/180C Fan/Gas 6 and make a crumbly topping by rubbing the breadcrumbs together with the butter and Parmesan, then dot and sprinkle on top. Cook for about 30 minutes, or until piping hot all the way through. Loosely cover the dish with foil if the topping is getting too brown at any stage.