This comforting soup can be made with fresh tomatoes or canned tomatoes.

Melt the butter without browning in a medium saucepan. Add the onion and cook 7 minutes over low hea, stirring with a wooden spoon. Remove the saucepan from the heat.
Add the tomatoes and sugar, bring to a boil and remove from heat.
Add the baking soda and stir until a foam forms and disappear.
Add the 1 1/2 cups of milk and bring to a boil, stirring frequently.
In a small bowl, whisk together the cornstarch and the 1/2 cup of milk, add to the soup and simmer for a few minutes, stirring with the spoon until the soup thickens.
Season with salt and pepper and serve.