Cut the tomatoes, onion, and chili pepper. Put them in a small pot and start cooking at a low temperature.
Add the vinegar, stir, and cover.
Let it simmer for about 10 minutes.
Once all the vegetables are soft, add the spices. Stir and then cover again.
Let it simmer for another 5 minutes.
Remove the cover and use the immersion blender to create a smooth and thin sauce.
If you don’t have an immersion blender, you can mash the tomatoes (see the notes below on those extra directions).
Let the sauce simmer until the rest of the meal is ready.
If the sauce gets too thick, use water and/or more vinegar to thin it out.
Spoon desired amount onto your dish.