Put the potato chunks in a 3-quart / 2.8 L saucepan and cover with cold water by 5 cm / 2 inches. Add a pinch of salt.

Bring to a boil over high heat, then lower to a simmer. Cook for 20 to 25 minutes, until a knife slides into the potatoes with no resistance.

Reserve 1 cup of the cooking water, then drain the potatoes. Let them sit for 2 minutes so extra moisture steams off.

While the potatoes cook, mash the garlic and 1 1/4 tsp salt into a smooth paste using a mortar and pestle, or grate the garlic finely and mash it with the flat of a knife.

Mash the warm potatoes with a potato masher until smooth. Don't use a food processor, it turns the starch gluey and the dip loses its texture.

Stir the garlic paste into the mashed potatoes until evenly mixed.

Drizzle in the olive oil a little at a time, stirring constantly, until it's fully absorbed and the mixture looks glossy.

Add the lemon juice and vinegar and stir until combined.

Loosen the dip with 2 to 4 tbsp of the reserved potato water, a tablespoon at a time, until it's smooth and thick enough to hold its shape on a spoon.

Taste and add more salt if needed. Transfer to a bowl, drizzle with a little extra olive oil, and scatter parsley on top before serving.