This tomato soup may well be the easiest soup to make in existence. Requiring only four ingredients (five including water) and only about 5 minutes of active cooking time, you don't even need a blender to yield delicious, vibrant results.
Heat olive oil in a large saucepan over medium-low heat until shimmering. Add onion and a generous pinch of salt and cook, stirring occasionally, until they are very soft and translucent, but not brown, about 5 minutes. Add garlic and cook, stirring constantly, until very fragrant, about 30 seconds.
Pour in tomatoes and 600ml (2½ cups) of water (I fill the cans will water to get the rest of the tomatoes out), stir to combine and bring to a boil.
Reduce heat to low, cover and simmer for one hour, until the flavours have mellowed and melded and the tomatoes have taken on a sweetness.
Turn off the heat and, using a potato masher, mash the tomatoes until very smooth. Serve immediately.
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Notes
If you prefer a creamy tomato soup with a very smooth texture, then you can absolutely use either an immersion blender or regular blender in step 5. Alternatively, you can pass it through a fine mesh sieve.