This dish combines two of my favorite go-to summer foods—lobster and cold soup---in the same bowl. The creamy potato and leek-based mélange is brightened with lots of fresh tarragon as I find the herb seamlessly compatible with crustaceans.
large Yukon Gold or other waxy potatoes, peeled and cut into ½-inch dice
large leeks, trimmed, tough greens removed, well-washed, and finely sliced
unsalted lobster stock (or substitute unsalted vegetable stock) plus additional milk—or use cream for a richer soup-- for thinning if needed
Combine the potatoes, leeks, milk and stock, salt, pepper, and parsley in a large saucepan or stock pot and bring to a simmer over medium-high heat.
Reduce the heat to medium-low, partially cover the pan, and simmer until potatoes are very, very tender (beginning to fall apart is fine) 20-30 minutes.
Use a potato masher to roughly mash about half of the potatoes.
Add the thawed peas and cook for about 1 minute to heat through.
Remove soup from heat and let cool to room temperature, stirring occasionally (stirring prevents a skin from forming). To speed up the cooling process, you can place the pot in a large bowl filled with ice water. Once cool, add the lobster meat, and refrigerate the soup until thoroughly chilled.
Once chilled, thin the soup with more milk, if desired. I usually need about at least a cup of extra milk at this point. For a creamier, richer soup, thin with cream instead milk.
Adjust salt—you will probably need more-- and pepper and serve cold in chilled bowls, garnished with the minced chives and optionally with dollops of crème fraiche or yogurt.