Green garlic soup

When the green garlic scapes arrive at markets I make this cold summer soup, but not until I have eaten them as a vegetable in their own right, first. Mildly garlicky after being cooked at a boil for about 5 minutes, they have the unexpected texture of artichoke hearts...

Here's the soup:

1 Tbsp olive oil (I like butter if the soup is going to be served hot)
3 bunches garlic scapes (about 4 cups), tender parts chopped
1 bunch spring onions/scallions (about 2 cups), chopped
1 small potato, sliced

4 cups-plus chicken or vegetable stock
1/2 cup natural, preferably Greek yogurt
Squeeze of lemon juice
Salt and pepper

Sweat spring onions in  olive oil or butter. Add chopped up garlic scapes, saute another 4 minutes or so.  Add warm stock and potatoes. Simmer until all vegetables are tender. Add salt and black pepper to taste, and add the yogurt, stirring it in. Transfer to blender in batches and puree. If you are a patient person, or simply driven, with a fanatical streak of perfectionism, press through a sieve to make extra smooth. It should be easily pourable. Add more stock if not. Chill. Taste. Now add the spritz of lemon if it needs a little brightening. Serve with a little dollop of yogurt and snipped chives.

If you'd like it hot, I'd grate some parmesan over the top or float a toast boat with some melted cheese-of-choice on it...

(The picture below shows the first incarnation of the soup, with onion, too, but I find this is too much, so I no longer add it.)