In a saucepan sat on medium-high heat, cook the tomatoes with cinnamon and cloves in water (the water should cover around half of the height of the tomatoes) until the tomatoes start to soften.
While the tomatoes are cooking, peel the onion, halve it and thinly slice.
Let the tomatoes cool down a bit.
Blend the tomatoes in a blender with a bit of cinnamon (discard the rest), cloves, a pinch of salt, and a bit of cooking water.
Add more cooking water and salt if needed to reach the desired thickness.