Potato Leek Soup

Michael Eisenwasser

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A silky potato leek soup that uses leek green tops only (the white part is high in fructans) plus potatoes, broth, and lactose-free milk.

Prep 15 min

Cook 30 min

Serves 6

Gluten-free

Ingredients

• 2 tablespoons garlic-infused olive oil
• 2 tablespoons butter
• 3 cups leek green tops only, thinly sliced (about 325 g — dark green and medium green parts, no white part)
• 1.2 kg (about 2 1/2 lbs) Yukon Gold potatoes, peeled and cut into 1/2-inch cubes
• 4 cups (950 ml) low-FODMAP chicken broth or low-FODMAP vegetable broth
• 1 bay leaf
• 2 sprigs fresh thyme (or 1/2 teaspoon dried)
• 1 1/2 cups lactose-free whole milk (or 3/4 cup lactose-free milk plus 3/4 cup heavy cream for a richer soup)
• 3/4 teaspoon salt, plus more to taste
• 1/2 teaspoon black pepper
• 2 tablespoons fresh chives, thinly sliced, for garnish

Instructions

Prep the Leek Greens

1. Trim the root end off each leek and slice off the white part where the color turns pale. Save the whites for stock or compost. They're high in fructans, so don't use them here.
2. Slice the dark green and medium green tops into thin half-moons. You should end up with about 3 cups sliced, or roughly 325 g total for 6 servings (about 54 g of greens per bowl).
3. Float the sliced greens in a bowl of cold water, swish, then lift them out with a slotted spoon so the grit sinks. Drain well.

Sweat the Greens

1. Warm the garlic-infused oil and butter in a heavy pot over medium-low heat until the butter foams.
2. Add the leek greens with a pinch of salt. Cook for 8 to 10 minutes, stirring often, until the greens are soft and darker but not browned. Low heat keeps them sweet.
3. Stir in the bay leaf and thyme and cook 30 seconds more.

Simmer the Potatoes

1. Add the cubed potatoes, broth, salt, and pepper. The liquid should just cover the potatoes; add a splash of water if it doesn't.
2. Bring to a simmer and cook uncovered for 18 to 22 minutes, until the potato cubes fall apart when pressed with a spoon.
3. Fish out the bay leaf and thyme stems.

Finish with Milk

1. Blend the soup with an immersion blender until mostly smooth but with a little texture left. For a smoother soup, blend in batches in a standing blender with the lid vented. Don't over-blend; potatoes can turn gummy if you run the blender too long.
2. Return the pot to low heat. Stir in the lactose-free milk (or milk-and-cream blend) and warm through for 2 to 3 minutes. Do not boil.
3. Taste and adjust salt and pepper. Ladle into bowls and top with fresh chives.

Tips & Substitutions

• Use leek green tops only. This is the main thing to watch in this recipe. Monash tested leek whites and leek greens separately: the white part is high in fructans, while the green tops are low-FODMAP in measured servings (Monash lists about 54 g per serving). Weigh 325 g of sliced greens for 6 bowls to land each serving near 54 g. Use the whole dark-green and medium-green sections, and stop where the color fades to pale.
• Yukon Gold potatoes blend up smooth. Potatoes are low-FODMAP in typical servings, so use what you have. Yukons break down into a silky puree with a buttery color; russets work too but puree more starchy and glue-y if over-blended. Red potatoes stay waxy and won't puree as smoothly.
• Lactose-free milk vs. heavy cream. Lactose-free whole milk (Lactaid, Fairlife) is low-FODMAP at 1 cup per serve. Heavy cream is low at 1/2 cup per serve. A half-and-half split (3/4 cup each) gives a richer soup without stacking lactose.
• Check the broth label for onion and garlic. Most store-bought chicken and vegetable broths include onion, garlic, onion powder, or garlic powder, all of which are high in fructans. Use the homemade low-FODMAP chicken broth or scan labels for "no onion" and "no garlic."
• Wash leek greens twice. Grit hides between the layers. The cold-water float-and-lift method works better than rinsing under the tap, because the dirt drops to the bottom of the bowl and you lift clean greens off the top.
• Don't over-blend. Potatoes can turn gluey if you blend them too much. Pulse with an immersion blender until the soup looks mostly smooth, or run a standing blender in short bursts. Thirty seconds total is usually enough.
• Reheat leftovers gently. Lactose-free milk will curdle if you boil it. Warm over low heat, stirring, and pull the pot off the burner as soon as steam rises.

Why This Works

Use leek green tops. The fructans that make a traditional potato-leek soup not low-FODMAP concentrate in the white part. The green tops test low-FODMAP at 54 g per serve, so using only the greens keeps the classic leek flavor without the gut hit. This is one of the few ingredients on a low-FODMAP plan where part of the vegetable is low and another part is high — worth learning once and carrying into every recipe that calls for leeks, scallions, or spring onions (same rule: greens only).

Potatoes make the soup thick. Plain potatoes test low-FODMAP in typical servings, so they can bulk out the soup without you counting grams. That's why potato-leek, scaled right, is one of the easiest classic soups to bring back on a low-FODMAP plan — the bulk ingredient was never the problem.

Garlic-infused oil carries the allium note. The fructans in garlic don't dissolve in oil, so the infused oil brings the savory base flavor without the FODMAP load. It fills in for the sauteed onion that most potato-leek recipes start with.

Lactose-free milk keeps the creamy finish. Regular milk has a small low-FODMAP serving because of the lactose. Lactose-free milk has the lactose already taken care of and clears at 1 cup per serve — room to stir a full 1 1/2 cups into a 6-serving pot and still stay well under the limit.

Storage

Refrigerate in a sealed container at 40°F (4°C) or below for 3 to 4 days. Reheat gently over low heat, stirring often. Do not boil — lactose-free milk curdles under a hard boil. If you want to freeze this soup, freeze the broth-and-potato base before adding the milk, then thaw and stir in fresh lactose-free milk when you reheat. Pure potato purees thaw better than dairy ones; the dairy can split and turn grainy on the thaw.

Not sure about an ingredient? FODMAP Tracker includes a database of 1,000+ foods with FODMAP ratings to help you cook with confidence.