Five minutes. Ripe tomatoes at room temperature, torn basil, flaky salt, and oil good enough to drink. That is the whole recipe.
Tear the basil, never chop it — a blade bruises the leaf and the oil ends up on the board instead of in the bowl. Add it off the heat and at the last moment. If your basil has had cold nights at altitude, you will smell it across the room before anyone sits down.
Salt the tomatoes first and let them sit ten minutes. They will give up enough juice to make their own dressing.