In a large pot, melt 2 tbsp butter over medium heat.
Add chopped onion and cook until translucent.
Stir in 3 tbsp flour and cook for 1 minute to form a roux.
Slowly pour in 3 cups chicken stock and canned tomatoes while stirring.
Bring to a boil, then reduce heat to simmer.
Season with 1 tsp sugar, 3/4 tsp salt, and 1/4 tsp black pepper.
Optional: Divide soup and puree half or all to desired smoothness, then return to pot.
Prepare cheddar bay biscuit mix according to package directions.
Drop spoonfuls of biscuit batter into simmering soup.
Cover and cook 15-20 minutes until dumplings are cooked through.
Remove from heat.
Melt 2 tbsp butter and mix with seasoning packet from biscuit mix.
Brush butter mixture over dumplings.
Serve hot and enjoy!