If you want to wash the basil beforehand, you should do this briefly with ice-cold water (not under the jet!) And let the herb dry thoroughly, preferably overnight. However, by washing the delicate leaves, part of the desired aroma is lost.
Pluck the basil leaves into pieces and place in a bowl, cover with olive oil and seal airtight.
Let it steep for about 1 month in a warm, dark place, e.g. in the kitchen cupboard. Check weekly and stir if necessary so that the leaves stay below the surface, otherwise they could go moldy.
Finally, pour the oil through an unbleached coffee filter into an oil bottle (e.g. old, boiled glass bottle) and throw away the leaves.
If you like it decorative, put a few fresh basil leaves in the container beforehand.
The preparation seems tedious, but the oil is all the more aromatic and just as durable as pure olive oil. I like to use it for pasta, it tastes like fresh pesto with a little grated Parmesan! Of course, you can use any other herb instead of basil. There are no limits to your imagination!