Cold Zucchini Soup

My mom always used to make this for us when we were kids, and I hated it, I think because it was so green. But as an adult it's a favorite soup of mine.

ZUCCHINI SOUP WITH YOGHURT
3 lbs zucchini (about 4 large)
8 T butter (I used half this--I think 8 T tastes WAY too buttery)
4C coarsely chopped onion
3C chicken broth (I used vegetable broth so it would be fully vegetarian since there's dairy in it, so that makes it kosher)
1 garlic clove crushed
1 to 2 C plain yoghurt (I used one cup of greek yoghurt)
salt and pepper to taste
½ C chopped scallions or chives (I've never used this part, because I'm not a scallion fan, and I don't think the soup needs it.)

Trim off ends of zucchini. And cut into one inch cubes. Melt butter in deep saucepan and add onion. Cook stirring until the onion is wilted and golden. Add zucchini and cook stirring about one minute longer. Add chicken broth, garlic, salt and pepper. Cover and simmer about 5 minutes.

Cool slightly and blend in blender for one minute (depending on the strength of your blender and how much texture you like--it can come out really smooth or more textured). Chill and stir in yoghurt. Serve sprinkled with chopped scallions and chives.