Potato Leek Soup

A low FODMAP potato leek soup of Yukon Gold potatoes, leek greens, low FODMAP chicken broth, thyme, butter, and lactose-free milk.

Prep 15 min

Cook 40 min

Serves 6

Gluten-free

Ingredients

• 2 tablespoons garlic-infused olive oil
• 2 tablespoons butter
• About 4 cups leek green tops, 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. Compost the whites or save them for someone not eating low FODMAP; they're high in fructans, and the fructans leach into stock too.
2. Slice the dark green and medium green tops into thin half-moons. You should end up with about 4 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. The white part is high in fructans, while Monash lists the green tops as low FODMAP at 1 cup (75 g), and they test low even in much larger amounts. Use the dark-green and medium-green sections and stop where the color fades to pale.
• Yukon Gold potatoes blend up smooth. Yukons break down into a silky, buttery puree; russets work too but turn gluey if over-blended, and red potatoes stay waxy.
• Lactose-free milk or a milk-and-cream mix. Lactose-free whole milk is low FODMAP at 1 cup per serve. The richer split (3/4 cup each of lactose-free milk and heavy cream) works out to 2 tablespoons of cream per bowl.
• Check the broth label for onion and garlic. Most store-bought broths include onion or garlic powder, so use the homemade low-FODMAP chicken broth or a certified low FODMAP broth.
• Wash leek greens in a bowl, not under the tap. Grit hides between the layers, and the float-and-lift method lets the dirt sink while you lift clean greens off the top.
• Don't over-blend. Pulse with an immersion blender until mostly smooth, or run a standing blender in short bursts; thirty seconds total is usually enough.

Why This Works

Leek green tops. The fructans that make a traditional potato-leek soup high FODMAP concentrate in the white part. The green tops are low FODMAP, so using only the greens keeps the classic leek flavor.

Potatoes make the soup thick. Plain potatoes are low FODMAP in typical servings, so they can bulk out the soup. That makes potato-leek one of the easiest classic soups to bring back on a low FODMAP plan.

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 them. 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 is low at 1 cup per serve, so 1 1/2 cups across a 6-serving pot is well within it.

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, and do not boil, since lactose-free milk curdles under a hard boil. To freeze, freeze the broth-and-potato base before adding the milk, then stir in fresh lactose-free milk when you reheat.