60 grams (2.1 oz) butter
1 large onion, chopped
1 kilogram (35 oz) Italian plum tomatoes, skinned, coarsely chopped
600 milliliters (20 oz) vegetable stock, divided
1 pinch of baking soda
1 Tbsp sugar
Salt and pepper
150 milliliters (5.1 oz) cream
1. Melt the butter in a saucepan and fry the onion until translucent.
2. Add the tomatoes, 300 milliliters (10 oz) broth, and baking soda. Stir, bring to a boil, then reduce heat and simmer for 20 minutes.
3. Remove the pan from the heat, let cool slightly, and puree the soup in a blender.
4. Add the remaining broth and season with salt and pepper. Add the sugar, bring to a boil, and simmer for 15 more minutes.
5. Divide the soup into warmed soup bowls and stir in cream to taste.