In a large pot over medium heat, melt the butter. Sauté the onions for about 5 minutes until tender but not browned.
At this point if you have an immersion blender, continue to make the soup in the pot. Add beets, broth, lemon juice, honey, thyme, salt and pepper. If you need to simmer the mixture until the beets soften a bit more, go ahead and do that. When the beets are very tender stick the blender in and blend away until smooth.
If you want to continue with a food processor or blender, great – scrape the onions into a the machine of your choice, then add the beets, 1 cup of the broth, juice, honey, thyme and salt and pepper and puree until smooth. Return the mixture to the pot and add the rest of the broth.
Either way, after the mixture is back in the pot, you add the cream and heat over medium-low heat until the whole thing is hot. Or if you would like to serve it cold, just stir in the cream and chill the soup for a few hours.
Serve the soup in mugs or bowls with the chopped onion and sour cream.