In a large saucepan, melt the butter. Add the chopped onion and cook over medium-high heat until translucent.
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add tomatoes, baking soda and seasonings
Add the tomatoes, salt, pepper, baking soda, and oregano and bring to a boil. Reduce the heat and simmer uncovered for about 15 minutes.
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puree the mixture in a blender
Put the mixture in a blender (or use your hand blender) and purée. The soup turns into a vibrant orange color!
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pour soup through a fine-mesh sieve
Carefully strain the mixture through a fine-mesh sieve. Use a spatula to push it through.
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add the orange juice and cream
Return the soup to the saucepan over low heat and stir in the orange juice. Add the heavy cream and bring just to a simmer while stirring.
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slowly add a swirl of cream before serving
To create the swirl of cream on top, gently pour the cream on top of the soup before serving. Be careful because it will sink if it is put on too fast.