Step 1

Place the leeks in a large bowl and cover with cold water. Let stand for 5-10 minutes to allow any dirt to settle. After the 5-10 minutes, scoop the leeks from the bowl of water and transfer them to a sieve. The leeks do not need to be completely dry.

Step 2

In a large pot, heat the oil with the leeks over high heat. Add a pinch of salt. When you hear the leeks begin to sizzle, give them a stir, cover the pot, and immediately turn the heat to low. Cook covered for 10 minutes. Remove the lid, allowing any water trapped in the lid to drip back down into the pot. Give the leeks a stir.

Step 3

Add the potatoes and enough of the stock to cover the potatoes completely. Crack pepper over top. Season with a big pinch of salt. Bring to a simmer over medium heat, and cook at a gentle simmer until the potatoes are knife tender and beginning to fall apart, about 20 to 30 minutes. Add more stock or water as needed if the liquid level reduces too much.

Step 4

When the potatoes are done, use an immersion blender to purée the soup until smooth or transfer the soup to a food processor or blender and purée until smooth — if using a blender, be sure to allow the soup to cool somewhat before blending to avoid exploding lids. Add water or more stock as needed to thin the soup to the right consistency.

Step 5

Return the soup to the pot and add the cream. Stir to combine. Again, if the soup is too thick, add water or stock until it is the right consistency. Simmer for just a few minutes more. Taste and adjust with more salt and pepper to taste. To serve ladle the soup into bowls and sprinkle some of the herby bread crumbs over top (see below).

Step 6

In a large skillet, toast the bread crumbs with the olive oil and a pinch of salt over medium heat stirring frequently, until the crumbs are evenly golden, 5 to 10 minutes. Taste the crumbs for seasoning. Add more salt if you wish and pepper to taste. Add the herbs and the lemon zest, if using, and stir to combine. Toast for another minute; then remove from the heat and transfer to a serving bowl.