Colcannon (Irish Mashed Potatoes with Cabbage)

Method

1. 1Peel floury potatoes, such as Roosters or russets, until you have 1200 g of peeled potato, and cut them into chunks of about 5 cm so they all cook at the same pace. Put them in a large pot of about 5 litres, pour in cold water to cover them by 2.5 cm and add 2 tsp of the salt. Bring to the boil over high heat, then turn the heat down to medium and simmer for 15 to 20 minutes. They are done when a knife slides into the biggest chunk with no resistance and the edges are starting to crumble.
2. 2While the potatoes cook, put about 1.5 litres of water on to boil in a second pot, a saucepan of about 3 litres with one long handle, and prepare the greens. Pull the dark, tough outer leaves off a small Savoy cabbage, cut it into quarters, cut out the core and slice the quarters thinly across the grain. Weigh out 300 g of sliced cabbage. Trim the 6 scallions (spring onions) and slice them, white and green parts, into thin rings.
3. 3When the water boils, add 1 tsp of the salt and the cabbage and boil it over high heat for 3 to 5 minutes, until it has wilted and turned a darker green but still has a little bite. If it turns grey and soft, it has gone too far. Tip it into a colander and press out as much water as you can with the back of a large spoon, because water left in the cabbage makes the colcannon wet. Put the cabbage in a bowl with 25 g of the butter and cover it with a plate to keep it warm.
4. 4Pour the 200 ml of whole milk into the empty cabbage pot and add 50 g of the butter and the sliced scallions. Warm it over low heat for 3 to 4 minutes, until the butter has melted and the milk is steaming but not bubbling. The scallions soften in the milk and give it their flavour. Keep it over the lowest heat, without letting it bubble, until the potatoes are ready.
5. 5Drain the potatoes and put them back in their pot over low heat, without the lid, for 1 to 2 minutes, shaking the pot now and then. Stop when steam no longer rises and the outside of the potatoes looks dry and floury. Water left on the potatoes makes the mash loose and watery.
6. 6Take the pot off the heat. Mash the potatoes with a potato masher, pouring in the hot milk with the scallions a little at a time, until the mash is smooth, with no lumps, and soft enough to drop slowly from a spoon. Don't use a blender or an electric mixer, which work the potatoes too hard and make them gluey. Taste, then season with up to the last 1 tsp of salt (less if your butter is salted) and the ¼ tsp of ground black pepper, and fold in the cabbage with its butter until the green is spread evenly through the potato.
7. 7Pile the colcannon into a warmed serving dish, press a hollow into the middle with the back of a spoon and drop the last 25 g of butter into it to melt. Serve straight away while it is hot, and let everyone dip each spoonful into the butter. Put any leftovers in the fridge within 2 hours.