In a large pot, melt 2 tablespoons of unsalted butter over medium heat until bubbly. Add the chopped onion and cook for about 5-7 minutes, stirring occasionally, until it becomes translucent and fragrant.

Sprinkle in 2 tablespoons of flour, stirring constantly for about 1 minute to cook off the raw flour taste.

Gradually whisk in 4 cups of chicken broth and 2 cans of diced tomatoes, ensuring a smooth consistency. Increase the heat to bring the mixture to a gentle boil, then reduce to a simmer.

Once simmering, incorporate 1 teaspoon of sugar, along with salt and black pepper to taste. Let the soup simmer uncovered for about 15-20 minutes.

For a velvety finish, carefully puree the soup in batches using an immersion blender or a standard blender.

In a separate bowl, prepare the biscuit mix according to the package instructions, integrating in 1 cup of shredded cheddar cheese.

With the soup still simmering, spoon the cheddar biscuit batter into the pot, making small dumplings. Cover the pot and let cook for 15-20 minutes.

Once the dumplings are done, remove the pot from the heat. Melt another tablespoon of butter and mix it with the seasoning packet from the biscuit mix if you like; brush it over the hot dumplings.

Ladle the comforting tomato soup into bowls, ensuring each serving gets a generous portion of fluffy dumplings.