Put the vinegar in a saucepan with approx. 0.25 l of water and bring to the boil with the tomatoes and a generous pinch of sugar. Let the whole thing simmer for about 7-10 minutes, making sure that the tomatoes are not too soft.
In the meantime, finely chop the rosemary needles.
When the tomatoes are soft enough, drain them over a sieve and collect some of the cooking liquid. Put the drained tomatoes in a bowl and mix with the chopped rosemary needles. Let cool a little and then squeeze in the garlic.
Pour 3-4 tablespoons of the cooking liquid over everything and stir. Finally add the olive oil and mix everything again.
The tomatoes should steep for at least 24 hours, preferably 48 hours.