Cook squash and onion in broth over medium high heat until tender-about 15 minutes.
Puree the contents of squash, onions and broth in blender. Do in small batches, as to not burn yourself with the hot liquid.
Return the pureed mixture to the pot and add the half and half. Cook on medium low for 3-4 minutes.
Remove one cup of the mixture and pour in a separate bowl. Slowly wisk in the sour cream to the separate bowl, as to not curdle the soup. Return the soup/sour cream mixture to the pot.
Season with salt and freshly ground pepper. Distribute between bowls and sprinkle with fresh dill. Serve immediately.
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