These onions are a revelation, and the very definition of low effort/high impact.
Two things are vital, though: the roasting tray must be big enough to fit 16 onion halves (if not, roast fewer, decreasing other ingredients proportionally) and these must be basted well, so they remain moist. Serve spooned over toast, mashed potatoes or rice, or with roast chicken.
Serves 6 as a side
8 medium onions, skinned (1.2kg)
4oz (100g) unsalted butter, melted
4oz (100g) white miso paste
Heat the oven to 500F/gas 10. Halve the onions lengthways, trim tops and a little off the bottom (you want the halves held together at the base).
Whisk the butter, miso and 2.1 pints (one litre) of warm water until fully combined.
Space apart the onion halves, cut side down, in a 16″ (40cm) x 11″ (28cm) high-sided baking tray or dish.
Pour over the miso water, cover tightly with foil, bake for 35 minutes, then remove foil and turn onions cut side up.
Baste well and cook, uncovered, for 45 minutes, basting every 10 minutes, until very soft and deep brown.
Carefully transfer to a platter, pouring the sauce over. Serve at once.