Honey and Spice Butternut Squash Soup

2 lb. onion, chopped
2 oz. unsalted butter
6 large garlic cloves
6 lb. cooked butternut squash, cubed
2 qt. + 1 cup chicken or vegetable stock
1 tbsp. cumin, ground
2 teaspoons salt
1⁄8 tsp. cayenne pepper
2 cups heavy cream
1 1⁄2 cups honey
3⁄4 cup sour cream
2 tbsp. cilantro, chopped