In a large saucepan, combine the tomatoes, sugar, salt, pepper and butter. Bring to a boil over medium heat, stirring occasionally.
In a small bowl, combine biscuit mix and milk. Drop batter in four mounds onto the tomatoes. Reduce heat; cover and simmer for 10 minutes or until a toothpick inserted in a dumpling comes out clean (do not lift cover while simmering).