Slender young leeks are ideal for this dish, not the baby ones that resemble spring onions, and certainly not fat, mature ones with tough stalks. I usually buy a bunch of four or five organic leeks that are just so tender once cooked that you can eat most of the dark green stalk. Also, make sure that your walnuts are new or current season, and ideally crack them yourself, as the shell protects the nuts and keeps them fresh.
Preheat the oven to 160˚C fan-forced or 180˚C conventional.
For the pickled onion, bring the vinegar, sugar, salt and about 50 ml of water to a simmer in a small pot. Add the currants and onion and bring back to a simmer. Remove from the heat and set aside at room temperature for at least 15 minutes, though longer is better, and an hour wouldn’t hurt.
Spread 100 grams of walnuts out on a baking tray and roast for around 15 minutes until golden and fragrant. Toss in oil and season. Set aside. Turn the oven up to 180˚C fan-forced or 200˚C conventional.
For the skordalia, bring the milk and 250 ml of water to the boil in a medium saucepan. Add the walnuts, sliced garlic and a pinch of salt, and simmer for 10 minutes. Tear in the bread and simmer for 3 minutes. Strain, reserving a little of the liquid, and add to a blender. Add the allspice, nutmeg, vinegar, oil and a pinch of salt. Finely grate in a little garlic to taste and blend until smooth, adding a little cooking liquid if needed. Cover and set aside at room temperature.
Place the leeks on a baking tray, drizzle with oil, season and roast for 25 minutes or until tender. Toss the asparagus in oil, season and add to the tray for the last 10 minutes of cooking.
To plate, smear some of the skordalia on a serving plate, arrange the leeks and asparagus on top, dollop on a little more skordalia, scatter over the walnuts, onion and currants, drizzle with a little oil and serve.