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Jerusalem Artichoke Soup with Brown Butter, Sage and Crisp Tuber Coins
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Jerusalem artichokes are sunflowers in disguise — tall, yellow-flowered *Helianthus tuberosus* that spends summer screening the fence line and autumn fattening knobbly tubers underground. From October onward, once the stems blacken, you dig them a forkful at a time, and the cold makes them sweeter. This soup turns that sweetness into something closer to velvet, with brown butter, fried sage and a scatter of the tubers themselves, sliced thin and crisped.
2 lb (900 g) Jerusalem artichokes, scrubbed but unpeeled
7 oz (200 g) floury potato (Russet, Maris Piper, Bintje), peeled and diced
1 large leek, about 7 oz (200 g), white and pale green only, sliced
2 fat garlic cloves, sliced
4 tbsp (55 g) unsalted butter, divided
3½ cups (850 ml) light chicken or vegetable stock
½ cup (120 ml) whole milk or single cream
1 fresh bay leaf
Juice of 1 lemon (half for the soup, half for acidulated water)
10 sage leaves
3 tbsp (25 g) pumpkin seeds
3 tbsp (45 ml) neutral oil, for frying the coins
Fine sea salt and freshly ground black pepper
The Recipe
Fill a bowl with cold water and the juice of half the lemon. Scrub the tubers under running water with a stiff brush, working into the knuckles where soil hides, then drop them straight into the acidulated water. Do not skip this: cut Jerusalem artichoke flesh oxidises within minutes, going grey-brown, and that discolouration carries through into the finished soup. Leave the skins on — they are thin, hold most of the nutty flavour, and the blender will take care of them.
Set aside one medium tuber for the garnish and slice it into coins no thicker than 2 mm (1/16 in), ideally on a mandoline. Pat them bone dry on a cloth — any surface water will spit in the oil and steam the slices limp instead of crisping them.
Heat the neutral oil in a small pan over medium heat and fry the coins in a single layer for 2–3 minutes, turning once, until the bubbling slows and the edges turn pale honey. Lift them out while most of the slice is still blond: inulin caramelises fast and goes bitter the moment the colour deepens to chestnut. Drain on paper, salt immediately so it sticks to the hot oil film, and leave uncovered so they stay brittle.
In a heavy pot, melt 2 tbsp (30 g) of the butter over medium-low heat and sweat the leek and garlic for 8–10 minutes, stirring often, until the leek slumps and turns translucent with no hint of browning. You want the sound to stay a soft sizzle, never a crackle — scorched leek gives the soup a harsh, oniony edge that cream cannot hide.
Chop the drained tubers into rough 2 cm (¾ in) chunks and add them with the diced potato, bay leaf, stock and 1 tsp salt. Bring to the barest simmer — surface trembling, one or two bubbles breaking — and cook, partly covered, for 25–30 minutes. Keep it below a rolling boil: the long gentle heat is what converts inulin to fructose and makes the soup sweet rather than merely earthy. The tubers are ready when a knife tip slides through with no resistance at all; anything firmer will blend grainy.
Fish out the bay leaf and blend the soup hot, in batches no more than two-thirds full, for a full 60–90 seconds per batch. The texture shifts twice: first to a rough purée, then suddenly to something glossy that coats the back of a spoon. That second shift is the point of no return for silkiness — stop early and you get sand. For a restaurant-smooth result, push it through a fine sieve with a ladle.
Return the soup to low heat, stir in the milk or cream and the juice of the remaining lemon half, then taste. The acid is structural, not decorative: without it the purée tastes flat and heavy, and with it the sweetness snaps into focus. Add salt in ¼ tsp increments until the flavour stops tasting of starch and starts tasting of toasted nuts.
Wipe out the small pan, add the remaining 2 tbsp (25 g) butter and melt over medium heat until the foam subsides and the milk solids at the bottom turn the colour of hazelnut shells and smell biscuity, about 3 minutes. Throw in the sage leaves and pumpkin seeds and swirl for 30 seconds — the sage will hiss, then go quiet and translucent, which is the signal to pull the pan off the heat before the butter crosses into black. Ladle the soup into warm bowls, spoon the brown butter over, and pile the crisp coins in the centre so they stay above the surface.
