Prepare the potatoes: Place the peeled and quartered potatoes in a large saucepan or stockpot. Cover them with cold water by about 5 cm (2 inches). Add a generous tablespoon of salt to the water—this seasons the potatoes from the inside out. Bring to a boil over high heat. You'll see the water start to froth and the potatoes will release a starchy, earthy aroma.

Simmer until tender: Reduce the heat to a steady simmer. Cook for 15-20 minutes, until the potatoes are completely tender. The best test? Pierce a piece with a knife; it should slide in with absolutely no resistance, and the potato should look like it's about to fall apart. The colour will be a pale, creamy yellow. Do not let them boil aggressively, or they'll break up too much and become waterlogged.

Drain and steam dry: Drain the potatoes in a colander. This is a non-negotiable step. Let them sit in the colander for a full 2-3 minutes, shaking occasionally. You want to see the steam rising off them. This dries out the excess moisture, which is the enemy of a creamy mash. The texture of the potatoes will look slightly floury and matte on the surface.

Warm the dairy: While the potatoes are steaming, combine the milk, double cream, and the 2 cloves of garlic (if using) in a small saucepan. Heat over a low flame until it's just warm to the touch—think bathwater temperature, not hot. You should see tiny bubbles form around the edge, but no boil. This prevents the cold liquid from shocking the potatoes and making them gluey.

Mash the potatoes: Return the dried potatoes to the warm pot. Use a potato ricer or a food mill for the silkiest, most professional texture. If you don't have one, a hand masher will work, but press firmly and consistently until no lumps remain. The sound of the ricer is a satisfying, soft squelch. The texture should look like fluffy, fine snow.

Incorporate the butter and cream: Add the unsalted butter to the hot, riced potatoes. Stir gently with a wooden spoon until the butter is completely melted and the mash looks glossy. Then, slowly pour in the warm milk and cream mixture (discard the garlic cloves), stirring constantly. Stop when the mash is loose and creamy but still holds its shape. The colour will deepen to a rich, pale gold. Taste and adjust the seasoning with the white pepper and fine salt.

Finish and serve: Transfer the mash to a warmed serving bowl. Use the back of a spoon to create a decorative swirl on top. Dot the surface with a few small knobs of butter, which will melt into golden pools. Sprinkle with the fresh chives, parsley, and a generous pinch of flaky sea salt. Serve immediately while the butter is still glistening.