Butternut Squash Soup with yogurt

1 1/2 pounds butternut squash or other winter squash 3/4 teaspoon olive oil or canola oil 3 stalks celery chopped * 2 small onion diced 2 small carrots diced[...]

2 tablespoons butter or 2 tablespoons canola oil 1 large onion , chopped 2 large garlic cloves , sliced 1 tablespoon grated gingerroot 1 tablespoon mild curry[...]