2 tablespoons unsalted butter or extra virgin olive oil
1 yellow onion, diced
3 cloves garlic, roughly chopped
Three 10-ounce containers frozen spinach, thawed
Kosher salt and freshly cracked black pepper
1 Yukon gold potato, diced
8 cups chicken broth
2 cups heavy cream
1/4 cup sour cream
1 tablespoon thinly sliced chives
In a large saucepan or Dutch oven over medium heat, melt the butter. Add the onion and garlic and cook until it is translucent and starting to brown on the edges, about 3 minutes. Add the spinach and 1 teaspoon each salt and pepper. Taste the spinach and season with an additional 1/2 teaspoon salt, if needed. Stir in the potato and broth and bring to a simmer. Lower the heat to medium low, cover, and simmer until the potato is very tender, about 30 minutes.
Let the soup cool slightly and, working in batches, process in a blender until smooth, filling the blender no more than half full and removing the lid slowly after blending. Return the soup to the pot. Add the cream and return it to a simmer, then remove it from the heat.
Stir together the sour cream, 2 tablespoons water, and the chives. Ladle the hot soup into bowls and drizzle each with some sour cream mixture.