Heat butter in a large saucepan
over medium heat. Add leeks and
sauté for 5 min or until softened.
Add garlic and sauté for 1 min
longer. Add potatoes and stock,
turn heat to high and bring to a
boil. Reduce heat and simmer for
10 min or until vegetables are very
soft and flavours are combined.
Add spinach and cook for 1 min or
until wilted. Let cool for a few min.
Transfer soup in batches to a
blender and purée until smooth.
Adjust seasoning to taste.
Serve with a spoonful of yogurt
overtop and sprinkle with chives.