In a dutch oven or large soup pot over medium heat, melt the butter. Add the onion, stirring until cooked soft. Whisk in the flour and cook for about a minute.

In a separate bowl, stir together the broth and diced tomatoes. Gradually mix the broth mixture into the pot until completely smooth.

Stir in the sugar, salt, and pepper. Bring the mixture to a boil, then reduce the heat to a simmer. Cover the pot.

Remove the lid from the soup pot and reduce the heat to low. Use an immersion blender to puree the soup until smooth. Return to a simmer.

In a large bowl, combine the flour, sugar, baking powder, garlic powder, salt, and cayenne pepper (if using).

In a separate bowl, whisk together the buttermilk and melted butter. Pour this mixture over the dry ingredients and stir until moist. Gently fold in the cheese.

Drop dollops of the dumpling dough into the simmering soup. Cover and continue cooking for 15-20 minutes. Check the dumplings with a toothpick.

In a small pot, melt and stir together the butter, parsley, and garlic. Brush this mixture over the dumplings.

Ladle the soup into bowls, ensuring each bowl has dumplings. Serve with the leftover butter herb mixture for dipping if desired.