To begin, dice the onion. Melt the butter in a large pot or Dutch oven. Throw in the onion and cook until translucent.
Now dump in the diced tomatoes and stir to combine. Add the tomato juice.
Next - and this is important - in order to combat the acidity of the tomatoes add 3 to 6 tablespoons of sugar. Now, you'll want to start on the low side, then taste and add more as needed. Some tomatoes and juice have more of an acidic bite than others. (For what it's worth, and I realize it's not worth much, I use 6 tablespoons of sugar.)
Next, add 1 or 2 tablespoons chicken base to the pot. I added 3, and it wound up being a little too much.
Now you can add lots of freshly ground black pepper. Stir to combine, then heat almost to a boil. Then turn off the heat.
Add in the sherry if desired. Stir in the cream. Add the basil and parsley and stir.
Serve the soup warm.