In this article
On the first cold rainy Tuesday of every year, my father came in the back door, smelled the kitchen, and said tomato soup before he even had his coat off. My mother never opened a can of soup in her life. She opened a can of tomatoes, which she said was a different thing entirely, and in the time it took the grilled cheese to brown, she had a pot of soup thicker and sweeter than anything that ever came in a can.
The part that looked like a mistake came right before the milk. She stirred a small pinch of baking soda into the pot, and it foamed up so fast my brothers thought she had ruined supper. The question everybody asks is how much baking soda. The answer is 1/4 teaspoon for a 28 ounce can of tomatoes, and no more. It neutralizes part of the acid in the tomatoes, and that acid is what curdles milk the moment it hits the pot. Too little and the milk can still split; too much and the soup tastes flat and soapy. A quarter teaspoon, a quick stir while it foams, and then warm milk, and the soup turns silky and smooth.
Why this tomato soup works
- Canned whole tomatoes. Picked ripe and packed in their juice, they give a deep, consistent flavor all year.
- A quarter teaspoon of baking soda. It takes enough acid out of the tomatoes that the milk stays smooth instead of curdling.
- Warm milk. Warm milk added to hot soup does not shock it. Cold milk is the second reason cream soups split.
- Butter and a little sugar. Butter rounds the soup out and a spoon of sugar takes the sharp edge off the tomatoes.
Ingredients
Makes about 6 cups of soup, 4 large bowls. The measurements are in US cups with grams in brackets.
For the soup
- 4 tablespoons unsalted butter (57g)
- 1 medium yellow onion, chopped
- 2 cloves garlic, minced
- 1 can (28 ounces, 794g) whole peeled tomatoes with their juice
- 1 cup chicken or vegetable broth (240ml)
- 1 tablespoon granulated sugar (12g)
- 1 teaspoon fine salt
- 1/4 teaspoon black pepper
- 1/4 teaspoon baking soda
- 1 1/2 cups whole milk (360ml), warmed
- 1/4 cup heavy cream (60ml), optional, for the top
For the grilled cheese
- 8 slices white sandwich bread
- 3 tablespoons soft butter (42g), or mayonnaise
- 8 slices sharp cheddar (about 8 ounces, 225g)
Whole peeled tomatoes have the best flavor; crushed tomatoes work too. Measure the baking soda level with a measuring spoon, never a pinch from the box, since a heavy hand makes the soup taste flat.
How to make tomato soup
Make the soup
- Melt the butter in a heavy pot over medium heat. Add the onion and a pinch of salt and cook, stirring now and then, until soft and golden, 8 to 10 minutes. Add the garlic and cook 1 minute.
- Add the tomatoes with their juice, crushing them with a spoon, then the broth, sugar, salt and pepper. Bring to a simmer and cook gently, uncovered, for 20 minutes.
- Blend the soup until smooth with a stick blender, or carefully in batches in a blender with the lid vented.
- Return the soup to low heat. Stir in the baking soda. It will foam up; keep stirring until the foam settles, about 30 seconds.
- Slowly stir in the warm milk. Heat gently until steaming, but do not let it boil. Taste for salt and pepper.
Make the grilled cheese while the soup simmers
- Butter one side of each slice of bread. Lay 4 slices butter side down in a skillet over medium-low heat, top each with 2 slices of cheddar and close with the remaining bread, butter side up.
- Cook until deep golden underneath, 3 to 4 minutes, flip, and cook until the second side is golden and the cheese has melted. Cut each sandwich into triangles.
- Ladle the soup into bowls, swirl a spoon of cream on top and serve with the grilled cheese for dipping.
Tips that make the difference
- Add the baking soda before the milk, never after. Once milk has curdled, nothing brings it back.
- Warm the milk in a small pan or the microwave until it is warm to the touch before stirring it in.
- Keep the soup below a boil once the milk is in. A gentle heat keeps it smooth.
- Low heat for the grilled cheese: the bread browns slowly while the cheese has time to melt.
Variations
- Roasted. Roast the drained tomatoes with the onion and garlic at 425 degrees for 25 minutes before simmering, for a deeper, sweeter soup.
- Basil. Stir a handful of torn fresh basil into the soup before blending.
- Chunky. Skip the blender and break the tomatoes up with a potato masher instead.
- Without milk. Leave out the milk and baking soda for a bright, clear tomato soup.
Storage and make-ahead
Keep the soup covered in the refrigerator for up to 4 days. Reheat gently over low heat without boiling.
To freeze, make the soup through step 3, before the baking soda and milk, and freeze up to 3 months. Thaw, heat, then add the baking soda and warm milk.
Grilled cheese is best made fresh, while the soup heats.
Frequently asked questions
How much baking soda do I add?
1/4 teaspoon for a 28 ounce can of tomatoes. Stir it in before the milk and let the foam settle.
Why did my tomato soup curdle?
The acid in the tomatoes split the milk. The baking soda, warm milk and a heat below boiling all prevent it.
Will I taste the baking soda?
Not at 1/4 teaspoon. More than that and the soup starts to taste flat and slightly soapy.
Can I use fresh tomatoes?
Yes, in late summer. Use about 3 pounds (1.4kg) ripe tomatoes, cored and chopped, and simmer a little longer.
Cut the grilled cheese in triangles. They were always for dipping, whatever anybody said about manners.
Homemade Creamy Tomato Soup with Grilled Cheese (The Baking Soda Trick)
Old-fashioned creamy tomato soup made from canned tomatoes, butter and onion, with a pinch of baking soda before the milk so it never curdles, served with grilled cheese triangles. US cups with grams.
Ingredients
- 4 tablespoons unsalted butter
- 1 medium yellow onion, chopped
- 2 cloves garlic, minced
- 1 can (28 ounces, 794g) whole peeled tomatoes with their juice
- 1 cup chicken or vegetable broth
- 1 tablespoon granulated sugar
- 1 teaspoon fine salt
- 1/4 teaspoon black pepper
- 1/4 teaspoon baking soda
- 1 1/2 cups whole milk (360ml), warmed
- 1/4 cup heavy cream (60ml), optional, for the top
- 8 slices white sandwich bread
- 3 tablespoons soft butter (42g), or mayonnaise
- 8 slices sharp cheddar
Instructions
- Melt the butter in a heavy pot over medium heat. Add the onion and a pinch of salt and cook, stirring now and then, until soft and golden, 8 to 10 minutes. Add the garlic and cook 1 minute.
- Add the tomatoes with their juice, crushing them with a spoon, then the broth, sugar, salt and pepper. Bring to a simmer and cook gently, uncovered, for 20 minutes.
- Blend the soup until smooth with a stick blender, or carefully in batches in a blender with the lid vented.
- Return the soup to low heat. Stir in the baking soda. It will foam up; keep stirring until the foam settles, about 30 seconds.
- Slowly stir in the warm milk. Heat gently until steaming, but do not let it boil. Taste for salt and pepper.
- Butter one side of each slice of bread. Lay 4 slices butter side down in a skillet over medium-low heat, top each with 2 slices of cheddar and close with the remaining bread, butter side up.
- Cook until deep golden underneath, 3 to 4 minutes, flip, and cook until the second side is golden and the cheese has melted. Cut each sandwich into triangles.
- Ladle the soup into bowls, swirl a spoon of cream on top and serve with the grilled cheese for dipping.
