Melt the butter in a large stockpot or Dutch oven over medium heat. Throw in the minced onion and stock cubes/bouillon. Cook until the onion is soft and translucent, about 3 to 4 minutes.
Make roux. Sprinkle the flour into the pot and blend with the butter until smooth. Stirring constantly, cook for 1 minute.Bring to a boil.
Pour the tomato juice into the pot. Then, stir in the sugar, salt, and black pepper. Bring the mixture to a boil over medium-high heat.
Once boiling, add cream and reduce to medium-low heat and let the soup simmer for 10 minutes, until it has thickened. Adjust acidity and seasonings. Remove the soup from the heat and taste-test. If necessary, add more sugar to combat the acidity of the tomato juice and adjust the salt and pepper according to your preference.