Melt butter in a saucepan, add onions and celery, cook until tender and translucent.
Stir in flour to create a roux, cook 5–7 minutes until nutty.
Whisk in warmed stock, then add tomatoes, sugar, salt, and pepper. Simmer 15–20 minutes.
Blend until smooth with immersion blender. Strain if desired for extra silkiness.
Return to pot, stir in cream and cheddar until melted.
Adjust thickness with stock or milk; simmer 15 more minutes before serving.
